At the end of last season it was reported that Conte sent Costa a text message claiming that he no longer sees the Spain international in his plans.
The forward scored 20 goals to help Chelsea win the Premier League title, but it appears that his disruptive behaviour off the pitch has got too much for Conte.
The latest reports have claimed that there is no way back for Costa, who is believed to be wanted by his former club Atletico Madrid.
"This is as much to do with his attitude as his ability," Redknapp told Sky Sports News. "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."
Costa has scored 58 goals in 120 appearances for the Blues since joining the club in 2014.