The Red Devils are still waiting to win the Premier League title for the first time since Sir Alex Ferguson stood down as manager in 2013.
Manchester United have only managed to finish in the Premier League’s top four in two of the past four seasons to limit their appearance in the Champions League.
Mourinho has already spent in excess of £300m during two summer transfer windows so far following the £89m addition of Paul Pogba in 2016 before Romelu Lukaku moved to Old Trafford in a £75m deal this summer.
Manchester United suffered a surprise 2-1 defeat at the hands of Huddersfield Town on Saturday afternoon to leave the Red Devils five points behind leaders Manchester City.
Former Liverpool midfielder Murphy believes Manchester United have been guilty over underachieving given the resources available to the three managers since Ferguson’s retirement in 2013.
“They should be competing with what they spent,” Murphy told Sky Sports.
“They’ve really underachieved with what they’ve spent over the last few seasons.”
Manchester United signed Benfica defender Victor Lindelof, Chelsea midfielder Nemanja Matic and Everton striker Lukaku in deals worth in excess of £150m this summer.
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