Real Madrid coach Manuel Pellegrini has left Karim Benzema out of his squad for the leaders' match on Saturday at home to Sporting Gijon despite the France striker having recovered from a groin problem.
Second-placed Barcelona play at promoted Real Zaragoza on Sunday and victory for Real, who top the standings on goal difference, will put them three points clear of the champions.
Brazilian playmaker Kaka will also miss the match at the Bernabeu, along with fellow injury casualties Royston Drenthe and Mahamadou Diarra.
Pellegrini told a news conference on Friday the damage to an adductor muscle in Kaka's left leg was healing well.
Sporting coach Manuel Preciado said his mid-table side would play hard but fair against Real, whom they held to a 0-0 draw at the Molinon in October.
"We will play strong and hard but without causing injury, with legal weapons," Preciado said in an interview with Friday's Marca sports daily.
"For us playing every year against Madrid or Barca is a prize and we have to keep fighting until the end of the season so we can do it again next year," he added.
Barca midfielder Xavi and defender Eric Abidal are both recovering from injury and are almost certain to miss the match at Zaragoza.
Real and Barca have 65 points from 26 matches, and Barca have a goal difference of 48 to Real's 50, with the arch rivals due to meet at the Bernabeu in three weeks.
Barca defender Gerard Pique returns to Zaragoza after spending a year on loan at the club during the 2006/07 season, when he made his La Liga debut.
"We have to win in Zaragoza at any cost and take the first step (toward retaining the title)," Pique said at a news conference. "The team is on good form, like last season once we had got over the blip in February."
Pique's defensive partner Gabriel Milito believes the title race will go down to the wire this season.
"Madrid are in good shape but the most important thing is that we continue playing the same way we are," the Argentine told Barca TV on Friday. "We are very well prepared for the final stages of the season."
Third-placed Valencia, 18 points behind the top two, host in-form Almeria on Sunday after David Villa's hat-trick against Werder Bremen on Thursday fired them into the quarter-finals of the Europa League.
"We have always said how important Villa is," coach Unai Emery said at a post-match news conference. "A team doesn't just depend on one player but a player (like Villa) can help a lot."
Sevilla, who are three points behind Valencia in fourth, need to pick themselves up for Saturday's trip to Espanyol after Tuesday's surprise Champions League exit at the hands of CSKA Moscow.
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