Jose Mourinho has warned Luke Shaw he must put in the work to become Manchester United's first-choice left-back this season.
The 22-year-old made his first appearance of 2017-18 as a second-half substitute against Burton Albion on Wednesday, having been sidelined with a foot injury since April.
United eased to a 4-1 win in the EFL Cup match, but Shaw was criticised for a lack of effort by former defender Phil Neville, who accused him of "coasting" through the game.
Mourinho insists it is unfair to expect too much from the former Southampton man, but has challenged him to battle for his place.
"He has to work. Just that," he told a news conference ahead of Saturday's Premier League meeting with Shaw's old side. "You saw the same as I see.
"Are you asking if he plays [on Saturday]? No, he isn't. He has to work. He has to improve.
“Look, he doesn't play for six months. I'm not expecting him to arrive on Wednesday and be man of the match or to be running up and down for 45 minutes. It's a process. He doesn't play for a long time."
46' - We're back under way. One change for #MUFC at the break, with Shaw replacing Mata. Welcome back, Luke!— Manchester United (@ManUtd) September 20, 2017
"You have other players in the Premier League who are not starting matches and their managers just say they're not in the best conditions," he said.
"We're speaking about some of the best players in the league. I heard last week the Chelsea manager [Antono Conte] saying that. The Arsenal manager [Arsene Wenger] said that.
"The players are not in their ideas, they're not in the best form after important injuries. Luke had surgery and a long time without playing. I cannot expect him to be back and strong, strong, strong in his work."