Costa knows Tuesday's Champions League opponents well, having moved to Spain from VfL Wolfsburg where he played under Felix Magath who is now coach of Schalke.
The Portuguese told a news conference that he had given Valencia coach Unai Emery a few tips for the last-16, first leg match at the Mestalla.
"Raul, together with Huntelaar, are the stars of the team," Costa said. "Nevertheless the strength of Schalke does not really lie there but with the work they put in over 90 minutes.
"They never give up, they're strong at set pieces and counter-attacks and are physically very powerful. We have to focus, play our football, perform well and rely on a bit of luck."
Valencia have been in fine form in La Liga in recent weeks, winning six and drawing one of their seven matches since the start of the year. Saturday's 2-1 comeback win at Atletico Madrid lifted them above Villarreal into third.
"We have to keep in mind we are playing home and away and try to score in our stadium and avoid conceding," Costa said.
The two previous meetings between Valencia and Schalke at the Mestalla ended in draws.
The teams played out a 0-0 stalemate in the 2007 Champions League group stages and nine years earlier drew 1-1 in a UEFA Cup quarter-final second leg.
OUTSTANDING MATCH
Schalke are confident their 1-0 win over Freiburg in the Bundesliga on Saturday will raise spirits after a bad start to the year.
"We had an outstanding match and that will hopefully help against Valencia," said goalkeeper Manuel Neuer.
Schalke's new signings, Iranian midfielder Ali Karimi, Greece striker Angelos Charisteas and Anthony Annan, will be available on Tuesday although the Ghana midfielder could be the only member of the trio who starts the game.
Magath has been on a charm offensive to win back disgruntled supporters.
"The fans have been patient just like the team and that is evident on the pitch," he said. "We need this union and I hope it stays that way."
Probable teams:
Valencia: 13-Vicente Guaita; 2-Bruno Saltor, 17-Marius Stankevicius, 20-Ricardo Costa, 28-Jordi Alba; 3-Hedwiges Maduro, 5-Mehmet Topal; 7-Joaquin, 24-Tino Costa, 19-Pablo Hernandez; 9-Roberto Soldado
Schalke: 1-Manuel Neuer; 22-Atsuto Uchida, 4-Benedikt Hoewedes, 21-Christoph Metzelder, 13-Lukas Schmitz; 18-Jose Manuel Jurado, 40-Anthony Annan, 12-Peer Kluge, 17-Jefferson Farfan; 7-Raul, 25-Klaas-Jan Huntelaar
Referee: Aleksei Nikolaev (Russia)
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