Another dull performance has left fans frustrated at the lack of inspiration and puts the Red Devils 24 points behind champions Chelsea.
Redknapp believes Mourinho is playing with fire after prioritising the Europa League final and that defeat to Ajax will mean this season has been a disaster.
“It’s been a majorly disappointing season in the league,” Redknapp said in his Sky Sports column. “When you look at the United team and Jose says he is struggling for players, that team cost about £260m, I would want a lot more.
“I am sure the Man Utd fans would want more – more excitement and more attacking football. Watching United is hard work at the moment, it was hard at the weekend [against Tottenham] and hard work again today. It’s tough to feel sorry for him, I think his reputation rests on next Wednesday.
“If they lose it’s been a massively disappointing season. They are 25 points behind Chelsea, they are no better than last season, they look pedestrian at times, and there is no excitement.”
United round off the season on Sunday at home to Crystal Palace with Mourinho threatening to field a weakened side given the fixture is three days before the final in Stocholm.
The all or nothing fixture means victory will provide a back door entry into the Champions League and ultimately provide the former Chelsea boss some relief ahead of a second season at Old Trafford.