Manchester United manager Jose Mourinho defended his decision to prioritise the Europa League ahead of the semifinal second leg against Celta Vigo on Thursday.

Mourinho rested first-choice players in Sunday's 2-0 Premier League defeat by Arsenal and United's hopes of finishing in the top four are fading.

They lead Celta 1-0 from the first leg in Spain and victory in the final against Ajax Amsterdam or Olympique Lyonnais would seal a place in next season's Champions League.

"The situation is simple – 17 matches in seven weeks with 16 players is impossible. It was not a gamble, it was a simple decision. A decision based on common sense," Mourinho told a news conference on Wednesday.

United lost several key players to injury in April, including leading striker Zlatan Ibrahimovic and defender Marcos Rojo.

"When we lost these players in a period of seven matches in seven weeks it was the impossible job. It was not a gamble but a consequence of the situation we are in," Mourinho said.

United have never won the Europa League or its predecessor, the Uefa Cup.

"To be in the final would be very important to fight for the only trophy the club has never won before," Mourinho said.

"We will do tomorrow what we have done since the start of the season which is to fight hard."

If United fail to win the Europa League and finish outside the Premier League's top four they will not play in Europe's most prestigious club competition for the second season in a row.

"If we don't qualify for the Champions League, it's because we're not good enough for the Champions League," Mourinho said.

"We are giving everything we can, the players, myself, everyone that works around here. We are giving everything so, when you give everything, no problem.

"Nobody has more motivation than I have to try and win tomorrow."

United captain Wayne Rooney, the club's record scorer, did play against Arsenal and is fit to face Celta but his future looks uncertain after a frustrating and injury-hit season in which he has scored only seven goals.

"I've been at this club 13 years. I want to play football here," Rooney said.

"The more I can play, the better for me and the more I feel I can help the team.

"I have not thrown my toys out of the pram. This club will be successful under Jose Mourinho," the 31-year-old added.

"It is important to be back in Champions League. Realistically this will be difficult through the league."