Clermont received fresh injury concerns on Tuesday ahead of Saturday's crunch European Cup clash with Harlequins as Kiwi centre Regan King and France number eight Damien Chouly were both ruled out.
The news comes just a day after captain Julien Bonnaire and scrum-half Thierry Lacrampe were also ruled out of the crucial Pool 4 encounter.
Former All Black King, who will return to Welsh region Scarlets next season, pulled a calf muscle last week and will be out for six weeks, the club revealed.
Clermont said shoulder injury victim Chouly would also miss the game, although the player himself took to Twitter to reveal "nothing is broken", and added that he hoped to recover in time for Saturday.
On top of those absences, and that of regular first-choice scrum-half Morgan Parra, Clermont are also sweating on the fitness of lock Julien Pierre, who has a back injury, and prop Daniel Kotze, who suffered a partial shoulder dislocation during Sunday's 19-12 defeat at Toulouse.
Clermont said a decision will be taken on Pierre and Kotze's fitness at the end of the week.
On the plus side, Clermont are set to welcome back from injury centre Aurelien Rougerie (ribs), Portugal flanker Julien Bardy (ribs), Samoan back-rower Fritz Lee (chest), Canada lock Jamie Cudmore (knock) and flanker Alexandre Lapandry (ankle).
Clermont top the pool ahead of Quins by four points but the two sides meet in their penultimate game at Twickenham Stoop.
With only the group winners assured of qualifying for the European Cup quarter-finals, neither side can afford to lose this match.
Clermont's final pool match will be at home to Top 14 rivals Racing-Metro on January 19 while Quins will travel to Scarlets.