Yes i agree. Im not at the doom and gloom stage that some members on this site always seem to be but these injuries at the wrong moment could be the difference between Amad making it at Manchester United or not.
Diallo a full season at Feyenoord and developing under one of the best Dutch managers in Arne Slot would have been fantastic for his development. If you look at Feyenoord and Slot, many players developed very well during their period in Rotterdam. Instead he was injured and didnt play for the first half of the season before wasting the second half of the season at Rangers.
Last year was a good loan but now he already missed quite a few games and doesnt seem to return anytime soon. He has the perfect moment now to make a lot of minutes at the right wing with Antony, Sancho, Mount (?) and Greenwood not being options for various reason.
Young players do indeed need a bit of luck. They need to get a chance and usually they do get the chance because of injuries and he misses that moment. Amad is a talented player and he already showed some good moments (he did well against Milan if i remember correctly) but breaking into the team when everyone is fit is going to be difficult for any young player.