Real Madrid winger Vinicius Junior is out for up to six weeks with a hamstring injury, Spanish media reports said on Monday.

Los Blancos confirmed the Brazilian's injury in a statement but did not specify his expected absence time.

Vinicius limped off injured against Celta Vigo on Friday in Madrid's 1-0 win at Balaidos, which kept the team top of LaLiga with a 100 per cent record after three games.

The 23-year-old may not be fit by the time the Champions League starts on 19 September, and is set to miss important LaLiga matches against Real Sociedad and city rivals Atletico Madrid before then.

"(Vinicius) wanted to continue, so I don't think it was that serious. He tried, then it hurt a bit," said Madrid coach Carlo Ancelotti on Friday, with the injury turning out to be more serious than first thought.

Spanish reports said the forward would miss between a month and six weeks, potentially missing five matches, four in the Spanish top flight and one in Europe.