Ole Gunnar Solskjaer revealed he asked England not to pick Mason Greenwood before the Manchester United forward was withdrawn from the squad after breaching coronavirus protocols.
Greenwood and Manchester City's Phil Foden were forced to fly home from Iceland earlier this month after they were caught mixing with local women in the England hotel.
The pair had just made their England debuts in the Nations League victory over Iceland when video footage emerged of their breach of the bio-secure bubble which had been set up to avoid contact with the virus.
England boss Gareth Southgate admitted he couldn't understand their behaviour and axed them from the subsequent match in Denmark.
But United manager Solskjaer defended Greenwood and said he warned England that the 18-year-old needed a rest before the start of the new season.
"Yeah, of course I speak to Mason and I've spoken to Mason," Solskjaer said. "Of course, what we speak about and discuss will be between the two of us.
"The kid had a fantastic season. He's just come through. You come to the end of the season and we've had less than two weeks off and he's called up to the national team.
"I have to be honest enough to say I tried my best to give him a rest over the summer. That the club asked specifically and pointed out that he should have had a rest.
"He needs it mentally and physically after that season he had. First thing that happens is: one - he's called up, and two - he's right there in the press.
"We've done whatever we can to protect him and I will keep on helping him. I know that when he comes back into the daily routine of the club and what we do to him, he'll be fine."
Greenwood has been training with United after passing coronavirus tests and Solskjaer confirmed the striker is in contention to feature in United's Premier League opener against Crystal Palace on Saturday.
"Yeah, he's part of the group. With the testing and Covid protocols, he trained by himself for a little while. We had some tests done and as soon as possible he was with us. He's a big part of this group," Solskjaer said.
"This is where he feels at home. He's not comfortable, we challenge him, we've got people looking after him.
"We have to understand he's an 18-year-old kid who needs managing."
Earlier in the close-season, United captain Harry Maguire was handed a suspended 21-month sentence by a Greek court after being found guilty of assaulting a police officer, resisting arrest and attempted bribery during an incident on the island of Mykonos.
Maguire denied the offences and has launched an appeal which nullifies the conviction, but the defender still lost his place in the England squad for the Iceland and Denmark matches.
Confident Maguire can focus on football despite the off-field distraction, Solskjaer said: "The process will keep on going. Knowing Harry, he's a very strong character so hopefully he can put that apart.
"Naturally, as a human being it will be in the back of his mind what's happened this summer, and apart from that you've just got to see how it develops."
United have spent most of the close-season in an unsuccessful attempt to sign Borussia Dortmund forward Jadon Sancho.
The deal is still not completely dead according to reports, but Solskjaer would only confirm that United are still looking to strengthen after signing just Ajax midfielder Donny van de Beek so far.
"You know I can't say anything about other clubs' players out of respect to them. I can't speculate. But we understand that to get even further; one - we need to develop what we have, two - we're also looking to strengthen the team, of course we are," Solskjaer said.
"I've been in dialogue with the club. Of course, we're always discussing and hopefully let's see if we can bring anyone in."