Paris Saint-Germain are exhausting every avenue in their attempt to keep football's hottest prospect Kylian Mbappe at the club, but it seems the Frenchman is set to snub the deal in favour of signing with Real Madrid on a free.

According to Sky Sports, PSG have offered Mbappe a monthly salary of £4 million, a mammoth signing on fee in the region of £100 million and full ownership of his image rights - yet the 23-year-old is reportedly soon to be announced as Madrid's latest galactico.

It would be a groundbreaking transfer, gaining such an unbelievable player on a free. Transfermarkt estimate Mbappe's market value to be £144 million; however, we can absolutely assure you that should he have a full contract, signing the superstar would cost a hell of a lot more than that in reality.

Which got us thinking, could Mbappe to Madrid blossom into the greatest free transfer of all-time?

It certainly faces some stiff opposition. From Lewandowski to Bayern, and Pirlo to Juventus, so many of the world's greatest players have joined clubs under the Bosman law, but we think it has every chance of doing just that.

Don't take our word for it, though, check out what we believe to be the 15 greatest free transfers in football history.

15. Zlatan Ibrahimovic - PSG to Man Utd

After four seasons clearing up every domestic honour available in Paris, Zlatan finally journeyed to the Premier League. Fans and clubs alike waited on tenterhooks for the big Swede's arrival at the UK's largest club - and by god, he did not disappoint.

His first season saw him notch 28-goals as the club went on to win both the League Cup and Europa League. However, a rather unfortunate ACL-injury forced his time in Manchester to end prematurely.

Zlatan Ibrahimovic was so fired up as AC Milan close in on Serie A title he broke team bus window

14. Gary McAllister - Coventry to Liverpool

The Scotsman signed for the Reds at the ripe old age of 35, which, makes it an unusual piece of business when you think about it. Although, whilst his transfer might have been out of the ordinary, his impact was simply extraordinary and McAllister is yet to be forgotten at Anfield.

He is most fondly remembered for scoring a ludicrous 40-yard free-kick in the dying embers of a Merseyside derby, which secured a 3-2 victory for the Reds. However, it was his impact in the dressing room and tutorage of a young Steven Gerrard which proved most valuable.

Gary McAllister had an incredible season for Liverpool in 2000/01

Gary McAllister had an incredible season for Liverpool in 2000/01

13. Zlatan Ibrahimovic - LA Galaxy to AC Milan

Yep, Zlatan makes his return, much like he did in European football.

You're easily forgiven, if, when he joined LA Galaxy, you thought that was the last we would see of him on the continent. But in typical fashion, Zlatan never fails to pull off the unexpected.

And he has actually been quite the revelation since returning to Italy. In his first season with the club he bagged 15 league goals in 18 appearances.

This season the goals have dried up a bit, scoring just eight, yet his leadership skills have been pivotal as AC Milan head into their final game knowing a win would clinch their first Scudetto since 2011.

Zlatan Ibrahimovic celebrates at Manchester United
MANCHESTER, ENGLAND - DECEMBER 26: Zlatan Ibrahimovic of Manchester United celebrates after scoring his team's second goal during the Premier League match between Manchester United and Sunderland at Old Trafford on December 26, 2016 in Manchester, England. (Photo by Jan Kruger/Getty Images)

12. Jay-Jay Okocha - PSG to Bolton Wanderers

He was so good they named him twice... sorry, it's compulsory to say that when discussing the silky Nigerian.

Bolton secured the services of this magician from PSG in 2002, which understandably, caused quite the stir at the time. Okocha was an instant hit with The Trotters thanks to his absurd level of flair, but he was more than just a bag of tricks and captained the club to a League Cup final in 2004.

Two respectable finishes in the league of sixth and eighth provide another big green tick when you assess his time at club.

Most importantly, though, you could definitely appoint him the founding member of the 'streets will never forget' club.

Jay-Jay Okocha is a one of the most skilful players in history

Jay-Jay Okocha is a one of the most skilful players in history

11. Leon Goretzka - Schalke to Bayern

This man's stature in European football has grown much like his biceps in recent years, and the German now finds himself as one of the highest rated central midfielders on the continent.

A mainstay in the Bayern Munich team that clears up on the regular, domestically at least, he also won the Champions League with the club in 2019/2020.

Goretzka with Bayern

Goretzka with Bayern

10. Thiago Silva - PSG to Chelsea

This one might have been higher up the list if it wasn't for the Brazilian's age. Now 37, Silva joined the Blues at the end of the 2019/2020 season and has been a revelation across their backline.

Formerly well in the argument for the best centre-back in the world, Silva proved at Stamford Bridge that he still had what it takes to cut it at the highest level. He was also talismanic as Chelsea went on to lift their second Champions League.

Thiago Silva celebrates Chelsea goal

9. James Milner - Man City to Liverpool

Milner might not be as flashy and fabulous as many on this list, however, his impact is nearly unmatched. Klopp recently said that "nothing Liverpool have achieved would have been possible" without his reliable vice-captain.

It's the standards he sets both on and off the field which made him an exemplary football player.

James Milner

James Milner

8. Michael Ballack - Bayern to Chelsea

Wow, Ballack was a player, wasn't he?

The German was comfortably one of the best midfielders in the world when he joined Chelsea, although, he was maybe overshadowed by the attacking exploits of Frank Lampard in his time there.

Nevertheless, he was instrumental in Chelsea lifting three FA Cups, one Premier League and reaching the 2008 Champions League final.

Michael Ballack Chelsea

7. Joel Matip - Schalke to Liverpool

Man, Schalke just seem to hand top players to other clubs based off this list...

Matip has been a seriously underrated Liverpool signing and it seems that this season he is finally getting the plaudits he deserves.

The big centre-back signed in the 2016/2017 season and has been a mainstay at the heart of Liverpool's defence ever since. He has steadily grown alongside Virgil van Dijk to the point where, now, many regard Matip to be one of best defenders in the business.

Liverpool v Arsenal - Carabao Cup Semi Final First Leg

6. Esteban Cambiasso - Real Madrid to Inter Milan

After signing from Madrid in 2004, Cambiasso found himself as a player in northern Italy. He spent over a decade at the club, growing into one of the best midfielders in the game and winning countless honours with his new found love, including five Scudettos and a Champions League. Not too shabby, ey?

The Argentine will forever be remembered as one of Inter's most loved warriors.

Inter's 2008 centenary kit was creative
MILAN, ITALY - JANUARY 20: Esteban Cambiasso of Inter celebrates scoring during the Serie A match between Inter Milan and Parma at the San Siro Stadium on January 20, 2008 in Milan, Italy. (Photo by New Press/Getty Images)

5. Cafu - Roma to AC Milan

Imagine getting Cafu, one of the greatest right-backs ever lived, on a free?

AC Milan did just that after Cafu decided to move on from Roma in 2003. The Brazilian slipped effortlessly into a legendary AC Milan backline that included the likes of Paolo Madlini, Alessandro Nesta and Jaap Stam.

In his time with the Rossoneri, Cafu won the Serie A and the Champions League with the club.

Cafu AC Milan

4. Sol Campbell - Tottenham to Arsenal

Imagine the cheek... Campbell didn't just leave Tottenham, he ditched them for their arch-rivals, on a free!

Of course, his impact is stuff of legend. The Englishman was like a rock at the back for the Gunners and played a major role in the club's greatest moment - the invincible season of 2003/2004.

In his time with the club he won two Premier Leagues and three FA Cups - reckon he regrets it? We think not.

Thierry Henry and Sol Campbell

Thierry Henry and Sol Campbell

3. Paul Pogba - Man Utd to Juventus

Juventus made a right mockery of United with this one.

Sir Alex Ferguson let Pogba slip through his fingers at the United academy, so the Frenchman went continental and signed with the Italian giants of Turin in 2012.

Pogba won the league every season he was in Italy. He scored countless stunners from outside the box, turned himself into a physical specimen of a man and became one of the best midfielders in the world.

In 2016, he re-signed for United for a then world record fee of £89 million and hasn't been the same player since.

Paul Pogba Juventus

Paul Pogba Juventus

2. Andrea Pirlo - AC Milan to Juventus

Milan decided to let Pirlo go after more than 10 years of service because they believed he was effectively done. Whoever was behind that decision, well, we hope they aren't in the beautiful game anymore because that is nothing short of blasphemy.

Pirlo was extraordinary at Juventus. He was the architect of the Old Lady winning four consecutive Serie A, two Supercoppa Italiana titles and a Coppa Italia before leaving in 2015.

What a shocking error of judgement.

Pirlo with Juventus

Pirlo with Juventus

1. Robert Lewandowski - Borussia Dortmund to Bayern

Yeah, we get it, nothing new when it comes to Bayern snapping up all the Bundesliga's top talent.

But Lewandowski is different. The Polish hitman has racked up numbers that rival the might of Lionel Messi and Cristiano Ronaldo at the Bavarian club - 344 goals in 374 games is the only stat that is relevant in this case.

If Mbappe has a job surpassing anyone, it will be this man.

Lewandowski Bayern Munich
MUNICH, GERMANY - AUGUST 08: Robert Lewandowski of Bayern Munich celebrates after he scores his sides first goal from the penalty spot during the UEFA Champions League round of 16 second leg match between FC Bayern Muenchen and Chelsea FC at Allianz Arena on August 08, 2020 in Munich, Germany. (Photo by Matthias Hangst/Getty Images)

De Jong price agreed! (The Football Terrace)