Gareth Bale left Real Madrid's match against Malaga in the fourth minute on Saturday with an injury to his left calf.
Luka Modric, who has already missed three months of this season because of a thigh injury, also left the game with a knee injury in the second half.
Real Madrid coach Carlo Ancelotti confirmed the injuries after Real's 3-1 win at Malaga, but he downplayed their long-term significance.
The setbacks come four days before Real's Champions League quarterfinal second leg against Atletico Madrid.
"Modric has had a problem with his knee, and Bale his calf," Ancelotti said. "Now I can say nothing. We will see over the coming days. There is nothing to say.
"They are not completely discarded. I am optimistic then can play in the quarterfinal return game."
Initial reports in AS said that Bale has a possible calf muscle tear, while Modric faces five to six weeks on the sidelines with strained ligaments in his right knee.
Club spokesman Emilio Burtagueno said the team were "concerned" about both players and would have to wait for medical tests on Sunday to know the extent of their injuries.
"It's a bad moment for Bale to get hurt. We will have to see what the tests say tomorrow," Burtagueno said. "And Modric also worries us. When we only have four days before the quarterfinal return leg, it's not good news."
Bale sat on the Bernabeu turf while rubbing his left calf. Team doctors signaled to manager Carlo Ancelotti that he needed to come off.
Bale was replaced by Javier Hernandez as Madrid went on to beat Malaga. They remain two points behind league leaders Barcelona.
Real Madrid will already be missing suspended defender Marcelo on Wednesday, when they host Atletico with their tie poised after a 0-0 draw in the first leg.
Ancelotti left Karim Benzema out of his squad for the Malaga match as the striker received a knock in training on Friday. The manager said he hoped to have Benzema back for the decisive match against Atletico.
Information from ESPN FC's Dermot Corrigan and The Associated Press was used in this report.