Players were cracking so many jokes I knew they would be off their game, says Manchester United's Jose Mourinho

The Portuguese was immensely unhappy with his side's first-half performance against Saint Etienne on Thursday night

Mourinho wasn't best placed, despite his side's 3-0 victory (Getty)

Manchester United manager Jose Mourinho revealed on Thursday night that his players were cracking so many jokes in the dressing room before the Europa League tie with Saint Etienne that he knew they were going to be off their game when the match began.

Mourinho marched off for the half-time dressing room before the whistle was blown after an opening 45 minutes which he said was “so bad”. After the game he sounded a warning to his players that there would be teams of Champions League class waiting in the next round if, as expected, United’s 3-0 first leg win proves to be enough. Roma, Shakhtar Donetsk, Fiorentina and Lyons all enjoyed first-leg wins.

“I had the feeling immediately in the dressing room,” Mourinho said. “Too noisy. Too funny. Too relaxed. My assistants had the feeling in the warm-up, some of the guys were not really focussed and not having the right adrenalin in their bodies.” The Portuguese was appalled by an early poor Eric Bailly back pass that put Sergio Romero under pressure. He removed Marouane Fellaini at half time, sent on Jesse Lingard, and United improved after the interval, playing with more pace.

They were fortunate, with two of Zlatan Ibrahimovic’s three goals coming after a soft free kick and penalty which he won and scored from. “Zlatan is just doing his job, he’s a striker and goalscorer,” Saint Etienne manager Chrisophe Galtier said afterwards. “But despite his talent he was given favourable conditions to score his goals and help him on his way to that hat-trick.”

Mourinho - who will be without suspended Ander Herrera in France next Wednesday - said his players had to approach this competition with the same seriousness they apply to the Champions League.

“I know Champions League is a competition that everyone wants to play and win but we don’t play Champions League; we play Europa League,” he reflected.

He said there had been a little of the same complacency at times in the group stage. “But when we needed to win, we did it. We needed to win against Fenerbahce and did it, needed to win on the last night in Ukraine and did it. When focus is there we answer. Tonight I think first half was too relaxed. Saint Etienne had right intensity and created us problems.”

Mourinho claimed he would not be tempted to rest too many players in Saint Etienne. “I always respect football,” he said. “It can be nasty with you, I don’t want my tem to be punished so I will go with a strong team.

“If the first half [tonight] had been 1-1 game may have been different. If we progress and we beat Saint Etienne and go into last 16 then people will have the right attitude: lots of good teams. Some of results today showed big teams are there, Champions League teams will be there. So let’s do next Wednesday the next result and go for the next draw.”