"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," the club said in a statement.

Spanish media reported the Brazilian winger is expected to miss almost a month, which would also keep him out of the Champions League visit to Atalanta on December 10, as well as Wednesday's match at Anfield.

Vinicius played the full 90 minutes of Madrid's 3-0 win at Leganes in La Liga on Sunday, setting up Kylian Mbappe for the opening goal.

"The crazy calendar... now to recover," wrote the 24-year-old on social media platform X.

Real Madrid president Florentino Perez railed against European and world football governing bodies UEFA and FIFA respectively on Sunday for their expanding match programmes.

The Champions League this season features eight group matches instead of six and an extra round which some teams will participate in if they finish outside the top eight.

Madrid have various players out injured for long periods, including Dani Carvajal and Eder Militao with severe knee injuries, which Perez blamed on increasing numbers of matches.

"This season we could play 82 matches -- there are 63 percent more matches organised by UEFA and FIFA, from 22 to 36," complained Perez.

"There have already been nine cruciate ruptures this season (in La Liga), the same as in the whole of last season. Specialists point to fatigue as the cause."

Vinicius has started the season in superb form, outshining summer arrival Mbappe thus far.

The forward, who finished second in the Ballon d'Or voting, has four Champions League goals in four appearances this season as well as eight La Liga strikes in 13 games.

Champions League holders Madrid have started their European campaign in shaky form, with two defeats in their opening four matches.

They lost 1-0 at Lille and 3-1 at home against AC Milan in their last outing in the competition, leaving them 18th in the expanded group table.

Liverpool, under new coach Arne Slot, lead both the Champions League table and the Premier League.