Defending champions Stade Français may have been hit by a serious injury just one game into the new Top 14 season.
Exciting centre Jonathan Danty was forced off in Sunday's 34-18 win over Pau.
Danty injured his left knee and is set to undergo medical tests on Monday to discover the extent of the damage.
"Jonathan heard something crack in his knee late in the first half," Stade Français boss Gonzalo Quesada told Rugbyrama afterwards.
"He tried to leave the field but something was wrong. That isn't very reassuring.
"He will undergo some tests on Monday, but it doesn't look very good."
Losing the 22-year-old for a long period of time would be a major setback after his strong performances in the 2014/2015 campaign, in which he scored eight tries.