"Seeing Celta's trajectory in the Europa League, they definitely deserve respect for the second leg", Mourinho said after his side's 1-0 win at the Estadio de Balaídos, as quoted on United's official site.
However, the fresh concerns to Rashford and Young are the last thing Mourinho needed as they could now join Zlatan Ibrahimovic, Marcos Rojo, Luke Shaw and Timothy Fosu-Mensah in missing the Arsenal game. Next week, big match at Old Trafford.
Marcus Rashford's stunning 67th minute free kick earned United a 1-0 first leg win at the Balaidos Stadium.
Even with all the injury problems facing Manchester United right now, Jose Mourinho got his tactics spot on. United can still qualify for Europe's elite club competition by winning the Europa League.
'I am going to change my team to play against Arsenal, so I think Wenger will be really happy with me, ' says Mourinho.
'The players that are in accumulation, they are not going to play next weekend'. Also, we play at Old Trafford, in front of 75,000 people, so we have to give everything on Thursday.
Mourinho instead vowed to keep his key players as fresh as possible for the second leg of their Europa League semi-final against Celta Vigo on May 11 having claimed a vital 1-0 first leg lead in Spain thanks to Marcus Rashford's victor on Thursday night.
"I think 1-0 is a good result, it is not easy to win here", the Belgian midfielder told MUTV.
'It is still close, it is half-time, they are leading 1-0 and we have to go out and make the second-half count.
Asked if he will rest players at the Emirates on Sunday ahead of the second leg, he said: "The players that are in accumulation, the players that are with lots of minutes because we played nine matches in April and this one, so 10 matches in four-and-a-half weeks". "It's all about hard work and dedication, you know - he's just got to keep going now".
The Spaniards started well but once again United's failure to take their chances showed its ugly head, with Henrikh Mkhitaryan and Jesse Lingard producing excellent saves from Sergio Álvarez.