Atletico are trailing 1-0 from the first leg, but they will be thankful to still be within touching distance of Valencia after playing for more than an hour with a man less at the Mestalla following Thiago Motta`s red card.

"It`s the most important game of the season. We will treat the game against Valencia as though it was a final," said Valera.

"We are aware of what we are playing for. We have to score and we have 90 minutes to do it."

Both Atletico and Valencia go into the match on the back of Primera Liga defeats this weekend.

Atletico went down to fellow cup quarter-finalists Real Mallorca - the Rojiblancos` third reverse on the trot - while Valencia slumped to a 1-0 home loss against Almeria, increasing the pressure on coach Ronald Koeman.

Valera insists his team are still on track for a good season despite their recent poor form, saying: "We are fourth in the league, and we are alive in the UEFA Cup and the Copa del Rey. At the start of the season we would have taken that.

"It is true that we are not in a good spell, but we are calm and have confidence in ourselves."

Atletico and Valencia were not the only cup quarter-finalists to suffer setbacks at the weekend, with only Mallorca and Getafe - who play each other in the last eight - managing to pick up wins.

Barcelona, who are second in La Liga, were held 1-1 at Athletic Bilbao and are now nine points behind runaway pacesetters Real Madrid, while third-placed Villarreal are 15 points off top spot after going down 3-2 to Bernd Schuster`s men.

Villarreal pushed Real hard at the Bernabeu before succumbing to defeat, and they will probably have to produce a similar display to get past cup opponents Barca at the Nou Camp after only drawing their home leg 0-0 last Thursday.

"We made a huge sacrifice and we came into the match very tired from the game against Barca," said Villarreal coach Manuel Pellegrini after the Real defeat.

"They were fresher, clearly. Now we must get over this and continue along this line of play to be able to get through to the semi-finals of the cup."

Getafe will look to build on their 3-1 away league victory over Recreativo Huelva this weekend when they travel to Mallorca defending a 1-0 lead from the first leg of their last-eight tie.

In the other cup clash, Racing Santander hold the biggest advantage as they go to Athletic's San Mames stadium boasting a 2-0 lead.

The matches at Atletico Madrid and Mallorca take place on Wednesday, while the games at Athletic and Barcelona will be contested on Thursday.