Manchester United manager Jose Mourinho has urged the fans to show "the best of Old Trafford" in the second leg of the Europa League semifinal next month.
United play the first leg in Spain on Thursday, and Mourinho wants the atmosphere for the return to be memorable because his players are "not so confident" when they do not have the full backing of their home support.
The manager has largely been impressed with the United fans since taking over in the summer, calling them "amazing" in his programme notes for the game against Swansea on Sunday.
But after the 1-1 draw he questioned whether the supporters had done enough to lift the players, who are tiring after a long season.
"It's very important that the players are strong mentally and enjoy a difficult atmosphere here and then to wish that at home we get the best out of Old Trafford," Mourinho told MUTV.
"When we get that our team has been phenomenal but when we didn't get that the team was not so confident. Let's hope we can have that at Old Trafford."
European semifinals have generated some of the best Old Trafford atmospheres, particularly against Barcelona in 2008, while Mourinho has been involved in Champions League semifinals with Porto, Chelsea, Inter and Real Madrid.
But it will be a new experience for many of his United players -- something he says they will have to deal with if they are to reach the final in Stockholm on May 24.
"The most important thing is to be ready for the occasion and to cope well with the moment," he added.
"It's very normal to see teams and players reaching crucial matches and lose identity and not be mentally strong enough to cope with the pressure of the moment."