* Centre back fit for crunch game at Real Madrid
* Last chance to revive title bid, Martino says (Adds Martino comments)
BARCELONA, March 22 (Reuters) - Barcelona have Gerard Pique back for Sunday's La Liga 'Clasico' at leaders Real Madrid but captain and fellow centre back Carles Puyol has not managed to shake off a knee injury, the Spanish champions said on Saturday.
Pique missed last weekend's 7-0 home win over Osasuna with an ankle problem but is in the squad for the clash at the Bernabeu (2000 GMT), when third-placed Barca will seek to trim Real's four-point advantage and keep alive their bid for a fifth title in six years.
Puyol, who is leaving Barca at the end of the season, is recovering well and should return to training next week, Barca said on their website (www.fcbarcelona.es).
Real have a three-point lead over second-placed city rivals Atletico Madrid, who play at bottom side Real Betis earlier on Sunday (1600).
Barca coach Gerardo Martino said if his side failed to win on Sunday their challenge was probably over.
"This is likely the last chance we have because after this match there are only nine left, and it is not the same to be one, four or seven points behind," Martino, in his first season in charge at the Nou Camp, told a news conference.
"It would be very hard to overturn a seven-point deficit or even a four-point one," the Argentine added.
"Not because we are not capable of doing so but because there are very few points still available and teams (fighting for the title) rarely slip up so much at this stage."
Martino said the key to Sunday's game would be preventing Real from having a chance to counter attack and thwarting in-form Portugal forward Cristiano Ronaldo, the La Liga top scorer, and Wales winger Gareth Bale, who is starting to come into form.
"We don't have to do anything different from usual as we go out in every game to win," Martino said.
"The crucial thing is to play well, keep possession of the ball, develop our game effectively, avoid losing the ball to prevent their counter attacks, and make sure Ronaldo and Bale have as few one-on-ones as possible.
"The two teams are coming into the match with very clear ideas about their playing style.
"The difference is that Real Madrid has been more consistent than us. We have not had the necessary consistency."
(Additional reporting by Elena Gyldenkerne in Barcelona; writing by Iain Rogers in Madrid; editing by Ed Osmond and Stephen Wood)