In a clear sign of United's shifting priorities as they approach the end of the campaign, Mourinho claimed earlier this week that he may well opt to rest certain key players against Arsenal in the Premier League on Sunday (7 April) before Celta Vigo visit Old Trafford for the second leg next Thursday.
Jesse Lingard accepts Manchester United's trip to Arsenal is a must-win match in the top-four race.
And United manager Jose Mourinho hailed his wonder kid who has stepped up in the absence of top scorer Zlatan Ibrahimovic due to cruciate ligament damage.
Merson believes the game comes at a flawless time for Arsenal as United have their sights set on winning the Europa League. Now, even winning the games doesn't guarantee us that.
I think this has been a good season and it can still be a very good season, ' insisted the United manager, whose side have already played 58 games this season.
In the pre-match press conference, Wenger did admit that it is a do-or-die situation for them.
Portuguese boss Mourinho questioned full-back Shaw's commitment and focus to the club last month and then said the player used "his body with my brain" after the 1-1 draw against Everton two days later.
"I think I try to respect everybody and I do not want to make a case of any person".
Rashford and United could have had more of an advantage to take back to Old Trafford for the second leg on May 11.
"He s a 19-year-old kid in love with football", said Mourinho.
But who are the players we reckon might make way at the Emirates and, therefore, might need removing from your side.
"More than focusing on the fact it is Manchester United, a big club and a big rivalry over the years, what is important is to have the chance to achieve our target".
Well-known Spanish football journalist Guillem Balague has told Sky Sports that Manchester United played well against Celta de Vigo in the Europa League on Thursday evening. "I think he will be really happy with me".
"If Celta was fighting for important things in La Liga we would go in same circumstances, but I can not go with the same team that played here and go again in the next Thursday".
The Gunners bid to finish in the top four is rapidly deteriorating and they find themselves six points off fourth placed Man City.
"We hope first of all that the statistics stay as they are, just two wins away from England", Celta coach Berizzo said.
Three-time European champions United had never reached the last four of the Europa League or its predecessor the UEFA Cup, while Celta were in their first major continental semi-final.