Jamie Redknapp thinks Diego Costa's attitude is the key reason behind his potential Chelsea exit.
Sky sources understand Costa won't play for Chelsea again after falling out with head coach Antonio Conte.
The 28-year-old was linked with a move away from Stamford Bridge in January and although he wants to stay at the club, Conte has lost patience with the striker.
Costa was set to return to the club's Cobham training base on Monday even with the uncertainty surrounding his future but has been excused from the start of pre-season training by the club.
Sky Sports News HQ understands Atletico Madrid are interested in re-signing Costa and are expected to make an offer for him.
And Redknapp, speaking in an interview with SSNHQ, thinks Conte has stamped his authority by not tolerating Costa's attitude.
"This is as much to do with his attitude as his ability," the former Liverpool midfielder said. "Antonio Conte's looked at him and thought he can't deal with him anymore. He's become too much of a handful.
"It's nothing to do with his ability or not being a good player, it's to do with disrupting the squad. Maybe his attitude just isn't right because there have obviously been a few clashes between the manager and the player.
"He's a sensational footballer but if you're a manager and you want a united dressing but one player upsets that, you have to get rid of him. And I'm sure that's why Conte's doing it."
Since Costa's arrival just under three years ago, he has become a key figure at the club, making 120 appearances and scoring 58 goals.
The Spain international has won two Premier League titles during his time in west London, playing a pivotal role in both successes and has a League Cup winners' medal to his name.
And Redknapp is concerned for Chelsea, claiming they could struggle to replace Costa with a striker of similar quality.
"I do worry about Chelsea now though because Costa was so good," Redknapp added. "These players are not easy to find.
"You could sign Alvaro Morata who is extremely talented but he doesn't get regular games at Real. When you are talking £50m to £60m, it is really difficult to find the players you want, who can make the difference Diego Costa did, especially with the style Chelsea play.
"They played with one up and Eden Hazard in behind him. It worked so well last season so to not see him in a Chelsea shirt will be hard for the players and certainly the fans because he's been extremely successful for them."