Reyes rues timing of injury
The Spanish ace picked up a knee injury after a late tackle by United midfielder Paul Scholes and it is feared that he could be missing for up to three weeks.
Reyes is a major doubt for Tuesday's UEFA Champions League second leg quarter final tie with Chelsea despite taking part in training on Monday.
The former Sevilla man admitted it would be a major blow to miss the game with Chelsea and especially a possible semi-final meeting with Real Madrid.
"The injuries never come well, but in this case the moment is more delicate because Arsenal has so much at stake," Reyes told Spanish daily AS.
"It is necessary to assure the league and to progress in the Champions League.
"To miss the quarter final game with Chelsea would hurt, but if we get through and played Real Madrid in the semi-finals, as seems probable, yes that would hurt me more."
Reyes did not want to blame Scholes for the injury despite Gunners boss Arsene Wenger criticising the tackle.
"It is part of the game, although he tackled me very hard," added Reyes.
"It could have been worse. I saw from the bench that it was very hard-fought and I was prepared for the worst."