Speaking to the club website yesterday, Aguero said he hoped his Olympic experience would help Atletico get through their moment of truth.

Atletico's Vicente Calderon stadium will be packed for the visit of Germany's Schalke 04 today in what is the most important night in the last 10 years of the club's history.

Spanish papers are referring to the clash as Atletico's "game of the century" as they seek to overturn a 1-0 defeat from the first leg and seal a place in the group stage of the competition.

Failure to beat Schalke would be a huge blow to the Atletico fans, whose side finished last season fourth in the Primera Liga.

Aguero was, of course, missing from the fist leg, played in Germany two weeks ago. But he has no doubt his side are able to overturn their first leg deficit.

"Atletico Madrid has to continue growing and it will be very important for us to take this step toward the Champions League. Once we are in the group stage we will be able to play the best teams in Europe, where we should be," said Aguero.

"The fans have to be confident in us, because next Thursday we will officially be a Champions League team," he said.

Aguero will go straight into the Atletico starting 11, where he will partner Diego Forlan in attack, meaning that recent signing Florent Sinama-Pongolle steps down to the bench.

The Spanish side will have one forced change in their side with Antonio Lopez out through suspension after his red card in Germany. Lopez will almost certainly be replaced by Mariano Perniaas coach Javier Aguirre looks to ensure a clean sheet.

"We know we have the score against us. But we are confident that we can turn things around. In order to win, we have to be calm," said Aguero.