The Red Devils head to Spain to take on Celta in the first leg next week as they chase a continental trophy in Mourinho's first season at the helm.
Asked about the home meeting with Swansea City on Sunday, Mourinho admits his squad is not at its strongest with injuries and suspensions but will do everything in their power to get a result before focusing on their European objective.
After tonight's 0-0 draw with Manchester City, Mourinho said: "It's going to be very difficult, it's very very difficult. But what can we do?
"We go with 11 and for sure the 11 on the pitch are going to give everything, that's for sure.
"So, we know we play our lives on Thursday in Vigo because we have to consider that the most important match of the season as we have reached a European semi-final.
"But against Swansea, with the support of Old Trafford, with these 24 matches unbeaten, we are going to go again and give everything."