The Spain playmaker had a relapse on a muscle problem when Barca were knocked out of the King's Cup 3-1 at home by Real in a semi-final second leg on Tuesday.
Xavi had just returned from a similar injury in his right leg two weeks ago in time for the games against AC Milan and Sevilla, and will be a doubt for Barca's Champions League last 16 second leg at home to Milan on March 12.
The leaders travel to the Bernabeu on Saturday with a 12-point advantage over second-placed Atletico Madrid, and a 16-point gap on the champions in third, but in need of a lift after their 2-0 reverse in Milan and the midweek defeat to Real.
"Against Milan and Real we weren't as inspired as we usually are, but we shouldn't be pessimistic," Barca's assistant coach Jordi Roura told a news conference on Friday.
"The team will step up and compete for everything. The attitude and the workrate of the players is commendable."
Tito Vilanova's number two said the squad had been hurt by Tuesday's defeat in front of their own fans, but that the best way to recover was "to compete and to get a good result."
Lionel Messi has recovered from an illness that saw him miss training on Wednesday, and Roura once again jumped to the defence of the Argentine, who has been questioned after a couple of poor showings.
The World Player of the Year, and Barca's leading marksman, failed to register a shot on target against Milan and Real, the only times this season that has happened.
"When you have the best player in the world, and he doesn't score, obviously you notice. But it is only an anecdote," Roura said of La Liga's top scorer with 38 goals.
"We have complete and absolute confidence in Messi. He can go as many games as he wants without scoring, because he will score again."
Messi has scored on three of his last four visits to the Bernabeu, and if he nets one more can equal the record goal tally for 'Clasicos' of 18 held by former Real great Alfredo Di Stefano.
