The summer signing has not featured in the PL since Matchweek 4 but won the club's Man of the Match award for an impressive performance in the UEFA Europa League on Thursday night - a display that may earn him a second start in succession.
"He just needs now to replicate this kind of performance in the Premier League," Mourinho told manutd.com. "The Premier League is different - he needs one more step. Obviously now confidence levels are higher.
"This performance gives him the right to believe that he can play the next match again and he needs to replicate this kind of performance in the Premier League with more physicality and more aggression."