I think it was a pretty bad decision by Rashford himself to continue playing while injured under the pretext of being there for the team. He continued playing to get selected for the Euros which was also a bad call because it meant he would only get a surgery after the Euros. So now he misses a fair chunk of games while he should have chosen surgery already in April. The league was in its final stages, Utd was pretty much secured of top 4, we could have missed him then. We can't miss him at the start of next season. Utd should opt for a title run, every point counts and I believe without Rashford for 10 games Utd will lose points and fall behind in the title race early on. I know the season is long but take into account how much points you need for a title win and then you realize every lost point is in fact quite dramatic.
It is not unfair to say he decided for himself and not for the sake of the team to opt for the Euros which sadly for him and England fans didn't work out fine. It is incomprehensible in my opinion for one main reason. There is a world cup next year. He could have reasoned logically and say "okay so I miss the euros but there is a world cup around the corner, England need a good Rashford not a half Rashford at the current euros so I will get my surgery now and not after the Euros." "This will also be good for Utd and the fans title ambitions next season".
What did he gain for playing months with an injury? His season ended in failure and he didn't play at the Euros.
So in conclusion every decision he made was wrong in my opinion. He wasn't at his best at the Euros which he could have seen coming judged by his final months at Utd and now he misses the vital start of the next season which could see utd fall behind early on. I fear Utd still isn't mentally challenging for the title, we still have the top 4 mentality.