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.
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