Real Madrid have confirmed Vinicius Junior will require a period on the sidelines after picking up a hamstring injury.
Vinicius played the full 90 minutes of Sunday's 3-0 win away at Leganes and did not appear to show any signs of injury during the game, although local reports state the Brazilian flagged a problem in the dressing room after the final whistle.
Quickly sent for scans on Monday, Vinicius has now been diagnosed with a hamstring injury. Real Madrid declined to offer a return timeline in their official statement.
According to MARCA, Vinicius is expected to miss around a month of action which, factoring in La Liga's winter break, means he would almost certainly not return before the end of the calendar year.
The injury comes as a massive blow for Madrid, who are battling to keep their Champions League campaign on track and face the unenviable prospect of a trip to Anfield to face Liverpool on Wednesday.
Madrid have already lost two of their first four games in the reformatted Champions League, whereas Liverpool are sitting pretty at the top of the table as the only side with a perfect record of four wins.
Carlo Ancelotti's side produced perhaps their best performance of the season at the weekend after a tactical tweak involving Vinicius and Kylian Mbappe. The pair had underwhelmed as a unit before swapping positions to face Leganes, with Vinicius starting at striker and Mbappe shifting out to the left wing. A 3-0 victory was a fair reward for Madrid's performance.
Mbappe could now return to a central role in Vinicius' absence or, if he remains on the left wing, Ancelotti could hand minutes to young striker Endrick, with fellow Brazilian Rodrygo still unavailable through injury.