Jose Mourinho believes Luke Shaw is going through a "difficult period" as he tries to break into Manchester United's starting XI.
Shaw has made just seven Premier League appearances this season, having missed most of 2015-16 due to a broken leg.
Questions have been raised over the England international's future as he battles to earn a spot in Mourinho's side, though the player's agent says he is happy at Old Trafford.
And Mourinho confirmed injuries and bad timing have hindered the 21-year-old's involvement to date.
"You try to have in the squad the players with more minutes, the players in better shape, in better condition," the Portuguese said.
"In Shaw'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."
United are on a 16-match unbeaten run in all competitions and sit sixth in the Premier League ahead of a trip to Stoke City on Saturday.