Louis van Gaal says he rested Marcus Rashford from Manchester United's 1-0 win at Norwich City to keep him fresh for the midweek trip to West Ham United. United struggled in the absence of Rashford to break down the hosts at Carrow Road, before a mistake by Sebastien Bassong allowed Wayne Rooney to set up Juan Mata for the only goal of the game.
The victory took United, who were also without the injured Anthony Martial, within one point of fourth-placed Manchester City.
"You see in the games, Marcus is not doing the things he did in his first match or second match anymore," Van Gaal explained to United's official website when asked about Rashford's absence.
"You want to deny that at first and you say it to him but then you see maybe it is tiredness.
"So I hope that these two games give him again the stimulus to be in the line-up in the next game because we have to play West Ham and it's not an easy game."
The Dutchman continued: "I wouldn't have rested him for the match [if there wasn't another one on 10 May], but now we only have two days' recuperation and recovery. That is too short for these players."
United will have Champions League qualification in their own hands if City fail to beat Arsenal on 8 May. They travel to sixth-placed West Ham on 10 May in the Boleyn Ground's final game.
Van Gaal said the Red Devils were now relying on Arsenal to do them a favour.
"I'm more or less a Gunners fan tomorrow, but it will be a tough game between these kinds of teams," the 64-year-old said.
Especially after the [Champions League semi-final] defeat to Real Madrid, it is not so easy for Manchester City to revive themselves."
United have won five of their six matches in all competitions and will face Crystal Palace in the FA Cup final at Wembley on 21 May.