The Red Devils slumped to their second Premier League defeat of the season last weekend following a 1-0 loss at defending champions Chelsea.
Alvaro Morata scored a second-half winner at Stamford Bridge to move Chelsea to within a point of second-placed Manchester United.
The 20-time English champions have only managed to win one of their last four games to leave Manchester United nine points behind leaders Manchester City.
Manchester United played out a goalless draw at Liverpool at the start of October before a surprise 2-1 loss to promoted side Huddersfield Town.
The Red Devils managed to beat title rivals Tottenham Hotspur 1-0 at Old Trafford thanks to Anthony Martial’s late winner.
Former Chelsea defender Desailly believes Mourinho still isn’t happy with the Manchester United squad.
He has to stay as Mourinho,” Desailly told Omnisport.
“He knows the capacity of his team.
“He looks like he’s not really had the team he wanted, like when you compare with [Pep] Guardiola, who really chose every player he wanted in and out.
“Mourinho, he’s still dealing with some players that he didn’t really want in his system.
“He’s doing well, so I hope United will shine like they were shining at the time with [Alex] Ferguson.
“But it’s tough. Every time, every game, there’s big history on the shoulders of all the players and on the manager. So, let’s give him time.”
Manchester United finished in sixth place in the Premier League table last season.
The Red Devils haven’t won the Premier League title since 2013 when Sir Alex Ferguson got his hands on his 13th top-flight crown.
Manchester United are in second place in the Premier League table and a point ahead of Chelsea and Tottenham Hotspur.
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