Maguire suffered an ankle injury during the Premier League clash against Aston Villa this month, and he has missed the next three games.
Speaking in his press conference today, Solskjaer revealed that Maguire has yet to return to running exercises, and he is unlikely to play against Villarreal.
The Norwegian tactician also confirmed that Anthony Martial will be on the sidelines, having yet to return to regular training after a knee injury.
The Red Devils face Wolverhampton Wanderers on the road in the final Premier League game of the campaign on Sunday afternoon.
They have received some positive news on the injury front with Fred and Scott McTominay available after overcoming minor knocks.
Daniel James is also in contention after a muscle injury. The Red Devils face Villarreal in the Europa League final in Gdansk on May 26.