Acknowledging the impact of a packed fixture schedule, Amorim admitted that his players struggled with fatigue in the closing stages of their match against Real Sociedad.
"We need to survive Sunday. The team was so tired in the last 20 minutes," said Amorim.
One of the biggest hurdles for United this season has been squad depth. Amorim acknowledged that his frequent squad rotations - particularly in Europe - have been necessary to cope with the physical demands of the season.
He added: "I think the biggest problem is to not have all of the players because, in the beginning, people talk about our rotation - especially in Europe, we are changing all the time. It’s because of this, because it’s really hard, and the Europa League is so much harder, in my opinion, than the Champions League. Not the games but the recovery to play Premier League on the weekend, so we have to deal with that.”