As I've said previously in this thread: I think the back injury has robbed him of his agility and explosiveness from a standing start, but the biggest concern of all with Rashford for me is that he either has no understanding of the team game, or he's not interested in it outside of a few link-ups per game. This is something that should improve season upon season for any player, but instead, as his physical ailments have worsened, he's gone backwards in this aspect as well, as he's trying to overcompensate and make even more solo/yolo runs now.
He tends to pass or cross as a last resort or because he's run out of space to continue a dribble; he rarely passes to players who are in better positions than him first and foremost and it's both maddening and concerning because there is no excuse for it. Players lose bits of their physical prowess all the time, particularly extremely fast wingers and forwards, but they adapt and change how they play, Rashford isn't even trying to do that and it doesn't seem like anyone at the club is forcing him to, either, and that, over anything else, should not be allowed to continue as he's detrimental to the team and kills so many attacks by not having any wits about him.
We have a number of players who do not see team-mates as foils - this is not a Rashford-only problem, but he is, without a doubt, the worst for it because he'd rather run down blind alleys than pass the ball, and he does it frequently enough for it to be something every single person watching him can be aware of and expect. That also means he is really easy for opposition managers to plan for and use an exploit to get at us, because on top of that blind alley running, when dispossessed, he is not bursting blood vessels trying to win the ball back, to the contrary, he'll stand there like it's not his job or responsibility to get that ball back, which usually leads to carries of over 40-50 yards up the pitch before that player or bunch of players face any impedance whatsoever.
At the moment, he's not just an offensive disaster - he's a complete defensive liability as well.