Don't think he's been injured allthat time though. I think the injury either occured or got a lot worse a little way through this season, as his performances (and contributions) massively dropped off. A fully fit Rashford wouldn't have spent Euro 2020 sitting on the bench while Saka was starting games...well maybe he would have with Southgate as manager, but the point is you couldn't really justify putting him in or near that team ahead of Grealish, Foden, Sancho, Sterling, Saka, etc. where as at his best he's an obvious first choice.
Have to say I'm a bit annoyed at both him and Ole. He's played half the season injured and now will miss a fair chunk of next season, just so he could go sit on the bench at the Euros and basically do nothing. How was that any help to his career, United or England? A Pep or Sir Alex would have told him absolutely ages ago to go get himself back to full fitness or not be picked, rather than play him in every single game for months even though he's half as effective as he should be and ends up coming off injured in half of them.