Manchester United isn't out of the race for a top-four finish in the Premier League, but the club has the second leg of a Europa League semifinal to play on May 11, and a not insignificant list of players ruled out of this match by injury or suspension.
Manager Jose Mourinho has said he will rest players for his team's match against Arsenal, and the squad he has brought to London suggests he wasn't bluffing. Mourinho risks incurring the Premier League's wrath: there are rules against clubs fielding weakened teams that might threaten the perceived integrity or quality of competition in the league.