Manchester United boss Jose Mourinho has paid tribute to Celta Vigo ahead of his team's clash with the La Liga outfit in the semi-finals of the Europa League.

Man United will travel to Vigo for the first leg of the last-four clash on Thursday night, before welcoming Eduardo Berizzo's team for the return match at Old Trafford next week.

Mourinho has branded Thursday's first leg "a difficult game", and has hinted that Celta will have the edge due to their "comfortable situation" in La Liga, in contrast to Man United's crowded Premier League fixture list.

"In a competition with so many teams, with very good balance, almost every team in the knockout phase was of the same level, they managed to be in the semi-final," Mourinho told reporters.

"I think that says everything [about Celta]. Because of their situation in La Liga, a comfortable situation, they also managed to think just about the Europa League, to rest players, to be in the maximum condition. It's a difficult game for us."

The winner of the Europa League trophy will gain an automatic spot in the group stage of the 2017-18 Champions League.