The Blues midfielder was part of the side that were beaten 3-0 by Wigan Athletic at home in the FA Cup quarter-final on Saturday, and Redknapp believes that the Belgium international needs to improve.
"I'm not convinced Fellaini is a top-four player and if he wants to be, he has to play better than he did against Wigan," Redknapp wrote in his column in the Daily Mail.
"His attitude, as well as his output, was poor when his team needed him. Since the January transfer window closed, Fellaini's performances have dipped."
Fellaini is Everton's record signing, after he moved from Standard Liege for £15m in 2008.