Rashford was desperate to leave Man United in the hope that he could return to his best form, and when Barcelona gave him the opportunity, he felt that it was time for him to shine again. Unfortunately, his hopes didn't quite pan out, and maybe he forgot that the fight at Barcelona was much tougher than at Man United. He was kicked out of Man United because of his attitude and laziness, so if he can't fix that problem, then things could get worse at Barcelona because there are so many great players there, and everyone has to fight for their place.
Going to Barcelona from United wouldn't solve the problem for him because he has failed to work on himself in order to improve his performance. I thought that he must have learned his lesson from what Amorim did to him but he hasn't, because he still show the signs of laziness in him and that's why he's finding it difficult to improve his performance. Maybe, we have already seen the best of Rashford and he has nothing to show us anymore.
It's not about being lazy. Rashford really wants to stay with the Barcelona team. He did a lot of fitness, like going to the gym. But he who has lost how good he used to play has lost it. It will be hard for him to get all that back. That's what Rashford is passing through. It's hard for him to accept that as reality that befalls him.
I think Rashford needs to take a break from football to rediscover himself rather than thinking that he is among the best players a team can have. That's what is deceiving him not to accept the reality that he is no longer in form.