Madrid: La Liga leaders Barcelona are racing to get defender Gerard Pique, who is recovering from a foot injury, back to full fitness in time for Sunday's visit of champions Real Madrid.
Pique worked in the gym on Friday and Vicente del Bosque later left him out of the Spain squad for their World Cup qualifiers.
"He is doing all he can to be ready," said Xavi on Friday. "He has gone 10 days without training so it is tough. I think it is 50-50 whether he plays or not."
With Carles Puyol out (dislocated elbow) midfielders Javier Mascherano and Alex Song are expected to reprise their unconvincing partnership at the back again.
Barca are two points clear of second-placed Atletico Madrid at the top of La Liga with a perfect 18 points from six games, and are eight ahead of sixth-placed Real.
"It would be a tremendous boost to morale to win," Xavi said. "It would be our seventh straight victory in La Liga and would leave Madrid 11 points behind us."
Real Madrid coach Jose Mourinho has no injury worries ahead of the 'Clasico', and his main concern would appear to be which of his creative midfielders to play.
Luka Modric, Mesut Ozil, and even Kaka, who made his first start this season against Ajax on Wednesday, are all competing for the playmaker role.
Atletico have the chance to go top with a win in Sunday's clash at home to third-placed Malaga and were boosted by a midweek 1-0 Europa League win over Viktoria Plzen, which came from a stoppage-time rocket by Cristian Rodriguez.
"A shot of such quality and decisiveness makes you happy. As I am a football fan I thought that was the best way to celebrate," Atletico coach Diego Simeone said of his manic, fist-pumping sprint down the touchline.
Atletico are expected to have top scorer Radamel Falcao back from a thigh strain.
Valencia head in to the city derby with Levante on Sunday deprived of midfielder Sofiane Feghouli who has been given a three-match ban after being sent off last weekend.
Their top scorer with three goals received the standard suspension for picking up two yellow cards in the 2-0 home win over Real Zaragoza, and an extra two-match ban for ironically applauding the referee's decision.
Athletic Bilbao's troubled start to the season continued with a 3-1 Europa League defeat at Sparta Prague on Thursday, and they host Osasuna on Sunday without a win in five matches in all competitions.
"The real problem is the current sporting situation," coach Marcelo Bielsa said when asked about media speculation surrounding his strained relationship with the squad.