Luke Shaw has struggled with a number of niggling injuries since returning from the broken leg he suffered 18 months ago.
He has not figured in a Manchester United squad since November 30 and questions have been raised about his future with Mourinho preferring to play Matteo Darmian – normally a right back – or Daley Blind in the left back position ahead of the former Southampton player, even when he has been supposedly fit.
But Mourinho insisted his decisions have been based simply on the physical condition of the players in his squad – and revealed that Shaw would have started the FA Cup tie against Reading on January 7 only to pull out because of illness.
Luke Shaw has struggled to impress Jose Mourinho this term
How Manchester United could look with defender signings worth £98m
Tue, January 10, 2017
Manchester United have been linked with moves for Kyle Walker, Danny Rose and Victor Lindelof, but how could Jose Mourinho's defence look with those players in his back-four?
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How Manchester United could look with a defence worth £98m
So even in that match, which could have been good for him, he was not able to play, so he's having a difficult period
"Of course his absence is about injuries," he said. "You try to have in the squad the players with more minutes, the players in better shape, in better condition.
"In Luke's case, even in the game against Reading, when he could have started the game and had 90 minutes, in the morning of the game he was ill and not ready to play.
"So even in that match, which could have been good for him, he was not able to play, so he's having a difficult period."
Jose Mourinho says Luke Shaw has had a difficult period at United
This week Shaw's agent Jonathan Barnett rubbished suggestions that Shaw will be off-loaded in the summer insisting: "Luke is happy with Untied and they are happy with him."
United go to Stoke today (Sat) with Mourinho saying he is only interested in wins, not merely extending United's 16-match unbeaten run, in a bid to close the gap on the teams ahead of them, especially with Manchester City and Tottenham facing each other today.
"I don't care about the unbeaten run." he added. "We not going to play any match to try to be unbeaten for one more match, or to try and reach 18 or to do try and reach 20, not at all. We want to win matches, we will try to win matches, we will risk to win matches.
"If we lose, we lose and we lose the unbeaten run. But we are not going to Stoke to defend our very nice unbeaten run.