Real Madrid coach Álvaro Arbeloa said Kylian Mbappé felt "discomfort" before asking to be substituted during Friday's 1-1 draw at Real Betis -- a result which was a major blow to Madrid's hopes of staying in the LaLiga title race.
Vinícius Júnior put the visitors ahead 17 minutes into the game at La Cartuja, but a 94th-minute equalizer from Héctor Bellerín saw the match end in a draw, leaving Madrid eight points behind leaders Barcelona, who visit Getafe on Saturday.
Mbappé asked to be withdrawn late in the second half and was taken off in the 81st minute, heading straight to the dressing room and being replaced by Gonzalo García.
"I have no idea [what's wrong with Mbappé]," Arbeloa said in his postmatch news conference. "He felt some discomfort. We'll see how he evolves over the next few days."
Sources told ESPN that initial indications are that Mbappé suffered a strain of his left hamstring.
Madrid next visit Espanyol on May 3, before their Clásico clash with Barcelona a week later.
Mbappé has scored 24 goals in 28 league appearances this season.
He is also set to be a key player for France at this summer's World Cup. France, finalists at the past two World Cups, will kick off their tournament June 16 against Senegal.
Madrid, meanwhile, have now won just one of their past six matches in all competitions.
"When games are so tight, these things can happen," Arbeloa said. "And we didn't have a lot of luck."
Arbeloa said Madrid should have been awarded a penalty kick, after Brahim Díaz's shot was blocked by defender Ricardo Rodríguez's hand at close range.
"It's a clear penalty, with the arm out," the coach said. "There isn't much else to see, it's very clear. ... They're decisions that affect the game a lot."