Real Madrid midfielder Toni Kroos is set for a spell on the sidelines with a knee injury.
"His recovery will continue to be assessed," said a brief Madrid statement released on the club's official website.
The Germany international has started 19 of Madrid's 22 league games so far this season, contributing four goals.
It is hoped that he will have recovered in time to aid Real's cause in the second leg of their heavyweight continental clash with PSG.
Kroos has helped the Blancos to Champions League glory in each of the last two seasons, so will be hoping to complete a memorable hat-trick.