"After tests taken today our player Vinicius Junior has been diagnosed by Real Madrid's medical services with a hamstring injury in his left leg," said Los Blancos in a statement.
The Brazilian star suffered the injury during his side's 3-0 win over Leganes on Sunday.
Spanish media reported the Brazilian winger is expected to miss almost a month, which would keep him out of the Champions League visit to Liverpool this week, as well as meetings with Girona and Athletic Bilbao in LaLiga and a clash with Atalanta.
Vinicius is the latest to join the club's lengthy injury list which includes key players like Rodrygo, Eder Militao, Dani Carvajal, Lucas Vazquez, Aurelien Tchouameni and David Alaba.
Real are second in the LaLiga standings on 30 points, four behind Barcelona who drew 2-2 with Celta Vigo on Saturday.
However, after two losses in their last three games in the Champions League, Carlo Ancelotti's side could be in trouble with a bad result at Anfield. They are 18th in the 36-team table with six points from four games.