The Red Devils have spent over £300m on new signings since Mourinho took over the reins from Louis van Gaal in May 2016.
Manchester United spent a world record move for Paul Pogba after he completed an £89m switch from Serie A giants Juventus in 2016.
The 20-time English champions have also brought in Henrikh Mkhitaryan, Romelu Lukaku and Alexis Sanches over the past 24 months.
However, the quartet have struggled to live up to their lofty reputations at Old Trafford since their respective transfers.
Manchester United will take on Chelsea FC in the FA Cup final at Wembley later this month after the Red Devils beat Spurs 2-1.
Former Liverpool FC captain Redknapp believes Mourinho’s big signings haven’t worked out at Old Trafford.
“The big-name players have not really worked for Jose,” Redknapp told Sky Sports.
“Whether they’d work for another manager, I don’t know, but they’re not working for Jose. He’s questioned the mentality of his team often.”
Manchester United have made significant improvement this term following a sixth-placed finish in Mourinho’s debut campaign.
The Red Devils are looking to win their third major trophy under Mourinho after success in the Europa League and League Cup last term.
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