Real Madrid's Portuguese internationals Pepe and Fabio Coentrao picked up leg muscle injuries in Sunday's shock 1-0 defeat at Levante, the club said.
In a medical bulletin posted on their website, Real did not say how long centre-back Pepe and midfielder Coentrao would be sidelined, although local media reported they would both be out for around two weeks.
Jose Mourinho's side, fifth with six points from three matches, play at Racing Santander on Wednesday.
Real need to improve their performances playing away against teams like Levante otherwise their bid to end Barcelona's three-year grip on the Spanish title will falter, according to left-back Marcelo.
"Against these kinds of teams, like Levante, and at stadiums like theirs, we fail too often," the Brazilian said in an interview published in Tuesday's As sports daily.
"The worse thing is that those points are those that make the difference at the end of the season," he added.
Champions Barca will not have Gerard Pique available for Wednesday's match at early pacesetters Valencia even after the Spain centre back returned to full training on Monday following a calf injury.
"Although he trained completely normally with the rest of his team mates he has still not been given the all-clear," Barca said on their website.
Midfielder Andres Iniesta and forward Alexis Sanchez, who have muscle tears, have been continuing their recuperation and are not expected back for several weeks.
Pep Guardiola's side have scored 15 goals in their opening three games, including an 8-0 humbling of Osasuna on Saturday.
Victory at Valencia, who have won their opening three games, would put Barca top, at least until Thursday when surprise joint leaders Real Betis, promoted at the end of last season, host Real Zaragoza.
Barca's Spain Under-21 midfielder Thiago Alcantara does not believe La Liga is a two-horse race between wealthy giants Barca and Real, who each earn close to 500 million euros a season.
"The 'League of Two' is a big lie," he told a news conference on Monday. "It has never been like that and it never will be. Teams come with a lot of desire, they get the best out of themselves and they come to win."
Valencia must not be scared of going after Barca on Wednesday and need to play to win, midfielder Sergio Canales, on loan from Real Madrid, said on Monday.
"Barcelona are perhaps the team who have made the least mistakes, but we have to search for them," the Spain Under-21 international told a news conference. "We must not be afraid of suffering a heavy defeat. We have to play knowing we can win."
Sevilla coach Marcelino has warned his players against underestimating Osasuna when they play there later on Tuesday as he believes the Pamplona-based side will be smarting after their thrashing at Barca.
"They are a team that use their weapons very well, with very engaged supporters, and they know how to eke out results at their stadium,"
