With Nemanja Vidic making the announcement last week that he will leave the club after ''eight wonderful years'' at Manchester United, the question I have been pondering since that announcement, and I'm sure I'm not the only one, is can he be replaced?
It will certainly be one of David Moyes's great challenges at the club as to whether or not he can find a replacement for Vidic, who has been a crucial part of United since arriving from Spartak Moscow in 2006.
Of course this is another worry Moyes must face with the club not only facing the thought of not getting Champions League football; they must now look to find a defender that will replace the great Vidic.
We will certainly get to see Moyes's real managerial skill should he be able to get Champions League football for the club and also find a suitable replacement for Vidic.
Some names have been tossed around as to who Moyes will purchase in the summer to replace the Serb, but there are only really five names that spring to mind - for me, anyway - when the question as to who will replace Vidic arises.
The first player Moyes should target and make it his mission to purchase in the summer is Giorgio Chiellini. The Italian central defender who currently plays for Juventus has been a crucial part in the Italian club's defensive setup for years now and has helped the club win many league titles and perform well in the Champions League in previous years.
He definitely has the leadership skills that Vidic has, as he has vice-captained Juventus for many years now. His raw skill as a defender has rarely been questioned and he has put in so many great performances for the club, making numerous goal-line clearances, and has made important tackles stopping teams from getting goals.
Also, like Vidic, he is very talented in the area - winning many aerial challenges and scoring goals in the air like the Serb has done at United.
The next player Moyes should think about bringing in is Cameroon international Nicolas N'Koulou. More of a long-term solution then Chiellini, this 23-year-old central defender has been playing his football at French side Marseille and has caught the eye of many clubs around the world with his great potential as a centre half.
Standing at just under six feet tall, he may not be the tallest defender but this does not take away from the potential skill this defender possess. His ground skills as a defender are impressive, he passes and controls the ball very well which is quite rare for a defender but he can also tackle and control the back-line, which is obviously crucial if you want to be a good defender.
He certainly possesses the potential to become a legend at United but he may not make the immediate impact that most fans would hope as replacement for Vidic but give him time and he would prove to the United faithful why Moyes purchased the player.
The third defender who I believe Moyes should be tracking right now is Eliaquim Mangala. This young Porto defender has recently become one of the most sought-after centre backs with a string of good performances for Porto over the past two seasons at the Portuguese club.
Mangala, who is only 22, is another long term replacement that Moyes can rely on to become a great player at United and maybe even a future captain.
Mangala is a very aggressive centre back who is not afraid to put his body on the line to win an interception or aerial challenge much like Vidic, he positions himself well which is crucial as a defender as he is able to clear passes shot into the box as he is in the right place at the right time. If Moyes wants this player though he would have to move quickly though with other teams looking to secure the services of the French national.
The next defender that I believe would fit into Vidic's boots is Marquinhos. This 19-year-old central defender made the move from Italian side Roma to big-spending French side PSG for a massive €31, - so obviously taking this player out of Paris would cost a fair amount.
But I really believe this player has the potential to become one of if not the best central defenders in the world.
At only 19, he has been a regular starter for PSG, giving fellow veteran Brazilian defender Thiago Silva a challenge for the starting spot at the club.
If Moyes is really looking for a long-term solution to Vidic leaving, this is the man to bring in.
His ability to predict which man an opposing player will pass the ball to is impressive as he is able to position himself so he is able to clear the ball out of danger. He also very rarely gives away fouls which is an important skill for a centre back to posses in the modern game. So if Moyes really wants this man he should act fast and snap him up this year.
The final player that Moyes should consider is Mats Hummels. The 25-year-old, who has quickly become one of the hottest central defenders in Germany, has been crucial in Borussia Dortmund's shoot to the summit of Europe's football teams with the club even put on the same pedestal as Barcelona and Real Madrid.
Hummels has arguably been the main piece in Dortmund's solid defence and has been linked with a move away from the German club many times over the past few seasons.
I really believe this is the perfect replacement for Vidic out of the list of names I have above.
The reason is because he will not only work out short term for the club but will also have a lasting impact at United.
Hummels is very much like Vidic based on build and height he is also quite good in the air and is very aggressive when it comes to tackling so I truly do believe he can become a united great and maybe even be a future captain.
But no matter who eventually comes into replace Vidic there is no question that he was one of United's greatest ever defenders and will go down in history as one of the best in Premier League history.
Write for GiveMeSport! Sign-up to the GMS Writing Academy here: http://gms.to/1a2u3KU