Real Madrid confirmed on Monday that forward Vinícius Júnior has sustained an injury to his left hamstring that will see him miss the team's crunch Champions League league stage trip to Liverpool on Wednesday.
Sources have told ESPN that Madrid hope the Brazil international will be out for between three and four weeks.
Vinícius, 24, played all 90 minutes of his team's 3-0 league win at Leganés. There was no indication from Madrid coach Carlo Ancelotti after the game that Vinícius was hurt.
The winger took to social media after the news broke, calling the football calendar "crazy."
Vinícius only returned to Madrid on Thursday after starting in Brazil's draws with Venezuela and Uruguay during the international break.
"Mbappé was fresher than Vinícius," Ancelotti admitted after Sunday's game. "He did very well with the goal, after a fantastic assist from Vini. Little by little the two are getting better."
Vinícius, who switched positions with Kylian Mbappé in Madrid's attack on Sunday, will miss several games, including Wednesday's encounter at Liverpool.
Madrid go into the game at Anfield on Wednesday in need of a win after losing twice in four Champions League games so far.
Los Blancos, who are second in LaLiga four points adrift of leaders Barcelona but with a game in hand, also have the FIFA Club World Cup coming up next month.
Mbappé, who was assisted by Vinícius for Madrid's first goal on Sunday, spoke of his growing partnership with the Brazilian forward.
"Vini Jr. and I read each other very well," he said.
"I've got a great relationship with him and he's a great player. The best players are here and we are ready to win a lot of games and trophies."
Vinícius has scored 12 goals and set up eight more in 18 league appearances for Madrid this season.
Information from ESPN's Gustavo Hofman and Rodrigo Faez contributed to this report.
