Athletic Bilbao goalkeeper Gorka Iraizoz insists that they do not think they have already beaten Manchester United.
Speaking to Sky Sports, the Bilbao shot-stopper admits that confidence is high after their first leg 3-2 win at Old Trafford in their Europa League round of 16 clash.
But they are not underestimating the English champions and Iraizoz admits their win in Manchester will count for nothing if they do not seal their place in the last eight.
"This tie has not been won," he told Sky Sports.
"Any 90 minutes in the San Mames is hard because the rivals change their system and we need to be focused from the first minute as an error could decide this.
"The atmosphere will be unique and it will be an incredible night for us to remember.
"I expect United to be more offensive as they need goals, that could be both positive and negative for us but we need to control the ball.
"The win at Old Trafford was historic, but we need to close the tie out and continue in Europe and then the enjoyment will be complete.
"But we must play without even knowing the 3-2 result from England, the coach insisting on us being mentally prepared."
Bilbao are also in the final of the Copa del Rey and Iraizoz says they want to win all they can this season.
"This is our first big final of the season, and we have prepared well," he said.
"There are a few guys with problems but in this type of match every player can increase their performance by 200 per cent on the pitch. So that won't be a problem."
Iraizoz has highlighted Javier Hernandez as one big threat that United will pose.
"Any United player in attack will be dangerous, although everyone assumes Wayne Rooney is the main danger but we have watched matches and the Mexican 'Chicarito' is deadly in these situations, and we must stop him," he said.
He also paid tribute to compatriot David De Gea, adding: "He really is a keeper with a huge future.
"In Manchester he was decisive in preventing more goals, he is young but I think he has an enormous future."