A trip to Arsenal awaits on Sunday and Mourinho could rotate his side given the match comes between European semi-final clashes against Celta Vigo, with Europa League glory offering Champions League qualification and a place in the history books.

Only Ajax, Bayern Munich and Juventus have won all three major UEFA trophies, including the now-defunct European Cup Winners' Cup, as well as the Club World Cup or the Intercontinental Cup.

United never tasted trophy success in the UEFA Cup, which evolved to become the Europa League from the 2009-10 season, and Mourinho is determined to end that wait.

"I know that it is the only competition that Manchester United as a club have never won," the Portuguese said. "And it would be great to close the circle and say, 'We are a club that won every single competition in the football world'.

"Thinking about us as a team, I think it would be a good achievement with so many problems we have and would allow us to be back to Champions League next season.

"So we have to try, that's what we are going to do, and honestly the Europa League for us now becomes more important.

"Of course it depends on the result, it depends on the way we analyse the situation tomorrow after the match, but if we have to rest players next weekend, we are going to do that."

Had it not been for a lack of cutting edge and a Premier League-high 14 draws, United would not be worrying about a top-four finish.

Mourinho also believes injuries and fatigue have had a lot to do with their struggles, meaning the return of Chris Smalling and Phil Jones after being injured on England duty in March could be too little, too late on the domestic front.

"In relation to the Europa League, it is very important they come in time," Mourinho said, having also confirmed Paul Pogba was back. "We have two matches in one week against Celta. It is important to have everybody back.

"In relation to the Premier League, I think it is too late because in the past month of April we played nine matches - seven of them in the Premier League and we had too many problems, we had too many players absent.

"Because of that, we had players that had to play 750, 800 minutes of football and we paid the price.

"We played against fresh teams and we were in accumulation (of fatigue).

"At this moment, the perspective is different because the Europa League becomes even more important for us.

"And it is good to have three players back, that gives us more options."