The Red Devils will welcome Swansea City to Old Trafford in the Premier League this weekend looking to record a fourth successive win.
Manchester United were 2-0 winners against Brighton and Hove Albion in the FA Cup last time out but Mourinho was critical of his players.
The 20-time English champions are 16 points adrift of runaway leaders Manchester City with eight games to go.
Manchester United lost 2-1 to La Liga giants Sevilla in the Champions League round of 16 despite a relatively kind knockout stage draw.
Swansea are unbeaten in their last five games in the Premier League to move clear of the relegation zone.
Former Arsenal defender Keown believes Manchester United boss Mourinho is facing a huge game against Swansea this weekend.
“This is quite a defining game for Mourinho against Swansea,” Keown told The Daily Mail.
“There was some harsh talk before the international break. He was critical of his players.
“Let’s see if there will be a response from those players. Can they win convincingly in the true traditions of Manchester United?”
Manchester United finished in sixth place in the Premier League table last term but Mourinho’s men won the Europa League and the League Cup.
The Red Devils signed the Chile international Alexis Sanchez in a swap deal from Arsenal in the January transfer window.
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