Chelsea have made some terrible mistakes when it comes to selling players over the past five to 10 years.

Allowing Romelu Lukaku to leave for Everton for £28 million in 2014 wasn’t particularly great business.

But the two worst deals, without question, involve Kevin De Bruyne and Mohamed Salah.

De Bruyne, who many football fans now regard as the world’s best midfielder, played just nine times for the Blues before being offloaded to Wolfsburg for just £18 million.

Salah, meanwhile, only made 10 more appearances than De Bruyne for Chelsea before being sold to AS Roma for £16 million.

The forward has scored 91 goals in 144 games for Liverpool since 2017 and would get into any starting XI in world football.

Today, De Bruyne and Salah are valued at a combined £216 million, according to Transfermarkt.

Salah, 21 at the time, was signed by Chelsea in January 2014 for £11 million, days after De Bruyne left west London for Germany.

The speedy winger had caught the eye at Basel, scoring nine goals in 47 games.

One of those goals was scored against Chelsea in the Champions League on November 26, 2013.

Salah netted the only goal in a 1-0 victory for Basel - and this, according to ScoutNationHD on YouTube, was the game that convinced the Blues to sign him.

You can watch his highlights from the match, which have been viewed almost two million times since being uploaded, here…

A constant threat whenever he received the ball, Salah forced Petr Cech into several saves on the night.

But Chelsea’s goalkeeper could do little to prevent the Egyptian from scoring the winning goal minutes before full-time.

This was Salah’s third goal in a row against Chelsea - a statistic that Jose Mourinho was acutely aware of.

"First of all, he won't score against Chelsea - which is a good thing," Mourinho said after sealing Salah’s signature two months later.

"But, speaking seriously, we had to react to the [Juan] Mata situation [Mata had just been sold to Manchester United]. We had to go for a young player, for a left-footed player and for a fast player - especially who is fast in the space because most of my attacking players are fast and fast with the ball.

"Salah is a kind of player that looks for the space and tries to get behind people so we think he was a good choice."

But why, then, did Mourinho not give Salah more of an opportunity at Stamford Bridge?

Speaking in 2018, Mourinho suggested that Salah wasn’t physically or mentality ready for top-level football at Chelsea when he arrived from Basel.

The Portuguese coach conceded that Salah had blossomed into one of the world’s finest players after leaving the Blues.

“I think he's developed incredibly well at every level,” Mourinho said. “Physically, amazing development. He was a fast, fragile boy and now he's a fast, strong man.

“He hadn't psychologically adapted, coming direct from a small club in Switzerland [FC Basel] to a big club in England and the Premier League [Chelsea]. It was too much.

”Now he plays everywhere against any team - completely different than the potential player we bought from Basel to Chelsea.

“He was a project player then and now he's one of the best players in the world.

“So I don't think the fact that I know him helps me, because I knew the project player and now he's a top player.“

But Mourinho’s comments were of little consolation to Chelsea fans, who must scratch their heads wondering how their club allowed both Salah and De Bruyne to leave having played so few games.

Salah scored two goals and registered four assists in his 19 games for Chelsea before being loaned to Fiorentina.

He then joined Roma on loan before completing a permanent move to the Italian side in 2016.

One year later he returned to England, signing for Liverpool and breaking the Premier League record for most goals (32) in a 38-game season in the process.