Solskjaer did want to secure Longstaff for his squad, but Newcastle put a huge price tag on his shoulders.
"I'm a firm believer that everything happens for a reason and I felt the same that night (captaining Newcastle), walking out and looking around," Longstaff explained, per the Manchester Evening News.
"If that move had happened, I'd never have been about for the Newcastle takeover and I'd never have been able to captain the club. There are so many things I wouldn't have been able to do.
"I'm happy it didn't happen in the end, because what I've gone on to achieve over the last two years - scoring in a League Cup semi-final, getting to play in a cup final, playing in the Champions League - have been things I never thought would happen, playing for Newcastle.
"When the Manchester United stuff came around, I was still so young. I'd probably deal with it differently now and not allow myself to get caught up in every little thing going on with it. I was coming back from my knee injury at the time, trying to get fit to prove I could still play. People are talking about you and have built you up so much that the perception is 'Now you're like Lionel Messi'. Everyone was expecting too much. Meanwhile, I was in the gym thinking 'I can't even do one leg squat'. There was so much going on, but none of the Manchester United stuff came to fruition and I seemed to go from up here to down there."