An outstanding breakthrough campaign saw the 18-year-old nominated for the PFA Young Player of the Year award and earn a first senior Three Lions call-up for the Nations League double-header in Iceland and Denmark.
Greenwood made his debut off the bench in England's narrow Nations League win in Reykjavik, where Manchester City playmaker Phil Foden also made his bow before things quickly went downhill for the duo.
The youngsters were caught up in controversy after flouting the strict bio bubble, leading to the pair being sent home, public admonishment from Gareth Southgate and a full FA investigation into the incident.
United also publicly rebuked Greenwood for his behaviour on a trip that Solskjaer does not believe he should ever have been on, stressing that people "have to understand he's an 18-year-old kid who needs managing".
"I've worked and the club have worked and all the staff here worked really hard," the United boss said.
"We gave Mason enough time on the pitch, we gave him exposure in the media. Then 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, we 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 1) he's called up, and 2) 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."
The PA news agency understands Solskjaer's comments came as a surprise to the FA. The governing body liaised with United before putting Greenwood up for the press conference, while England staff saw no problem including the 18-year-old following dialogue with clubs over the fitness and welfare of players.
Asked if the FA need to look more carefully at how they treat young players like Greenwood, Solskjaer said: "One hundred per cent. That's why I tried not to let him go this summer.
"But it's in their right to call him up. Then again, OK, you call him up, you don't have to put him in front of the world cameras first day, or second day – I don't know.
"When Mason says what he says – he did well in that interview, I'm not worried about that – but still it's drip feeding in, and I felt that he needed a rest more than being exposed to that environment.
"But I'm sure when he gets into this daily routine, club routine, he'll be back to his normal self."
Solskjaer's stance was strikingly similar to something you would have expected former United boss Sir Alex Ferguson to say on the subject.
But the Norwegian has spoken to Greenwood about the incident in Iceland ahead of Saturday's season opener against Crystal Palace.
"You learn that what you do will be (scrutinised)," Solskjaer said.
"I'm not saying he didn't make a mistake. Of course he's made some mistakes. But it's us, the grown-ups here as well, we need to make decisions that benefit him.
"I know Gareth is really, really keen on looking after players as well so I'm not worried about that."
Asked if he had spoken to Southgate before Greenwood's call-up and expressed his concerns, Solskjaer said: "I didn't. The club put, how do you say, a request into the FA, the club secretary did.
"It's just one of these feelings that you have for players.
"Of course I should have got hold of Gareth's number. He's not called me after either, so next time I'll speak to him and we'll discuss it."