Villarreal upbeat about Europa League
"We are coming into the match in a positive frame of mind," Valero told a news conference ahead of Thursday's quarter-final first leg against the Dutch side at the Madrigal.
"Although we lost (1-0) to Barca we gave a good account of ourselves and we could even have equalised near the end," he added.
"We'll try to continue in the same vein in the Europa League to get a good result and we are convinced we can win the competition."
Villarreal eliminated Bundesliga club Bayer Leverkusen and Napoli of Serie A in the previous two rounds and Valero said success against such big clubs had given his team a confidence boost.
"We have already knocked out important teams and we have no other choice but to go for it now," he said.
"We have to fight to the death in each game if we want to achieve our goal."
The second leg is on April 14 in the Netherlands and the winners will play Porto or Spartak Moscow in the last four.