Man United legend on Diego Costa: 'They are better off without him'
The Spaniard has living out in exile after falling out with fiery Italian manager Antonio Conte, despite the Blues winning the Premier League last season.
"They are better off without him," said Keane on ITV's Champions League highlights show. "The guy is obviously big trouble.
"I know he has done well for them, but he looks to me to be a bit of a balloon. Get rid of him. Have players at your club that want to be there."
Costa wanted to make the move back to Atletico Madrid after being told by text message that he was surplus to requirements by boss Conte.
Since then, he has refused to train and even claimed that the club are treating him like a ‘criminal’.
Chelsea dock his wages every week he does not turn up to training with the reserves.