Just one win from their last seven league matches has left the Red Devils in sixth position in the table - eight points behind fourth-placed Arsenal and 11 points behind leaders Chelsea.
Jose Mourinho's side have impressed in both the League Cup and Europa League this season, but Redknapp does not believe that the 20-time English champions are strong enough to launch a top-four challenge in the league.
"Man United aren't good enough at the moment, I look at the team and it doesn't excite me. Man United will do well to make the top four this year," Redknapp told Betsafe. "They will finish in top six but I don't know if they will make the top four."
Man United will attempt to return to winning ways in the league when they travel to Everton on Sunday afternoon, before welcoming Redknapp's former side Spurs to Old Trafford on December 11.