Spain goalkeeper Valdes, whose Barca contract expires in the summer, tore knee ligaments during the midweek win over Celta Vigo, ruling him out for the title run-in and the World Cup in Brazil.
Valdes, who has been at Barca for his whole career, announced he would leave the club in the summer, but could find himself injured and without a team if he did so.
Reports claim that Barca will offer him a short contract extension if this is the case, allowing him to get fit, but whatever happens he is unlikely to play for the club again.
"For him, the situation and what it means for us from here on, it is very bad news," playmaker Andres Iniesta said.
"Football and sport are like this. When you are playing each Sunday and Wednesday, for good or for bad, it doesn't give you time to savour moments or to have regrets. For this reason, we are Barca and we are mentally prepared to push to the limit.
"There is nothing for us to do other than look forward with who we have available. You cannot sit back as if you sleep then the rest will move ahead of you. We are back now in the title fight due to our own merits.
"There is a month and half to go and we will give everything."
Barca lie second in La Liga, one point behind Atletico Madrid with eight matches remaining. Real Madrid are three points behind their city rivals.
But Tata Martino’s run have the easier run-in, until they host Atletico in the final game of the season, which could well be the title-clincher.
And they should start by making light work of Espanyol, particularly with Lionel Messi back in form.
Espanyol are without a win in nine consecutive derbies against Barcelona (D2 L7), losing the last four without even scoring.
Los Periquitos have only won one of their last 11 home league games against their neighbour (D3 L7); 3-1 in January 2007.
In their four previous visits to Cornella-El Prat, Barca have scored eight goals and conceded just two.
Espanyol are unbeaten in two home league games (W1 D1); they have not gone three in a row unbeaten at home since September (W2 D1).
Barcelona have not kept a clean sheet in five away league games, their worst run since March 2013 (eight).
Barca have already lost three away league games this season; something that had not happened to them since 2008/09.
Javier Aguirre has only won two of his 16 league meetings with Barcelona (D2 L12).
Sergio Garcia has directly participated in a league-high 53% of Espanyol’s goals this season.
Neymar has scored nine goals in 22 La Liga games this season; that’s one more than Robinho managed in his debut campaign in Spain (eight in 2005/06).
Lionel Messi is the top scorer across the second round of games so far (14); he has netted twice as many as Cristiano Ronaldo (seven).
Barcelona have recouped a league-high 10 points from losing positions on the road this season.
Lionel Messi has played three league games at Cornella-El Prat so far but has never scored there.
Live European matches covered on Eurosport-Yahoo! this weekend (all times GMT):
Barcelona v Espanyol - 3pm Saturday
Athletic Bilbao v Atletico Madrid - 7pm Saturday
Real Madrid v Rayo Vallecano - 9pm Saturday
Bayern Munich v Hoffenheim - 2.30pm Saturday
Napoli v Juventus - 7.45pm Sunday
- Sports & Recreation
- Victor Valdes
- Lionel Messi