Sisi had two spells with newly promoted Valladolid before moving to Los Rojillos over the summer.
He retains a strong fondness for his former club but his loyalties are now with Osasuna, who lie bottom of the La Liga standings after nine games.
"For me it's a special game because I have much affection (with Osasuna), but in the field everything is forgotten," he told the club's official website.
"We must focus on ourselves. Winning would help us to gain confidence."
Jose Luis Mendilibar's side took their woeful start in the league into the Copa del Rey on Thursday as they slumped to a 1-0 defeat in their fourth round first leg clash against Liga Segunda outfit Sporting Gijon.
Sisi thought there were positives to take from the game but acknowledged they need to start winning in order to reduce the pressure on Mendilibar.
"The only negative (against Gijon) was the result," he added.
"Now all that remains are the results. It's what we have to take. We cannot be negative. You have to see the positive and think only of Valladolid.
"We have to take our minds off doubts and think that we're going to win no matter what."
Valladolid will be able to welcome Manucho back to the starting line-up after missing Monday's 2-2 draw with Real Sociedad through suspension.
Marc Valiente suffered muscle discomfort in Thursday night's 1-0 Copa del Rey win over Real Betis and is doubtful, as is fellow defender Carlos Pena with concussion.
Alvaro Rubio is banned, though, after receiving his fifth booking of the season so Juan Angel Neira is poised to replace him in midfield after impressing against Betis.
"I like the midfield position and, if I play, I will try to get a win in Pamplona," the Argentinian told the club's website.