The world and European champions have suffered a string of injuries which have contributed to their slight dip in form over recent weeks.
Carles Puyol's away goal in the 1-1 draw from the first leg last week gives Barca a slight edge against a team who have always made life tough for them.
"We play 11 against 11, there will be seven substitutes on the bench, and we are doing well," Guardiola told a news conference on Tuesday when asked about his possible team selection.
"It will be a game for men, it will be very demanding, and we'll need everyone to be at 100 percent."
Midfielder Sergio Busquets needed stitches in a gashed knee after Saturday's 2-1 league win over Real Sociedad while Ibrahim Afellay and David Villa are long-term injury victims.
"The most doubtful of the players is Busquets," Guardiola added. "Xavi is fine and Alexis is OK although he is still suffering a little.
"They have trained pretty well, we'll see how they are tomorrow."
Valencia coach Unai Emery, asked about Barca's cagey handling of injury news recently, replied: "It's a good strategy not to let on anything to your rival. If we knew, would it be an advantage?"
"If we don't make it, we remain alive in two competitions," Guardiola said. "We have a chance to play our fourth final this season and the players are aware of that.
"The quarters and semis have been very tough but we have responded in an extraordinary way."
