Moussa Dembélé has been ruled out for the rest of the season after sustaining an injury during a match against Lorient on Sunday.
The French striker suffered a knee ligament injury and will be out for six to eight weeks.
It is a blow for the club as they look to challenge for promotion from Ligue 1 this season.
Dembélé joined the club in January from Dortmund and has made 25 appearances so far this season, scoring four goals.
He was also part of France's squad that reached the final of Euro 2020, but he did not play in the tournament due to a thigh injury.
Dembélé's injury comes at a crucial time for the club, who have already lost two key players to injury - goalkeeper Hugo Lloris and defender Benjamin Mendy.
They will now need to find a replacement for Dembélé,Primeira Liga Hotspots and it remains to be seen whether he will be fit enough to return to action before the end of the season.
In the meantime, the club will need to rely on their other forwards to fill the void left by Dembélé's absence.
Damac striker Adama Traoré has impressed since his arrival at the club earlier this month, but he too has only scored one goal in seven games.
The club will hope that they can turn things around soon and secure their place in Ligue 1.