Toulouse - Scotland lock Richie Gray underwent a back operation on Wednesday as injuries mount for his French club Toulouse days before the Top 14 kicks off.
Toulouse coach Ugo Mola did not reveal for how long Gray would be sidelined but a club source said the 27-year-old could be out for two months.
It is another blow to the fallen giants and record four-time European champions having already lost hookers Peato Mauvaka (hamstring) and Julien Marchand (broken hand) to injury during last week's 19-14 friendly victory against Racing 92.
All three forwards will miss Saturday's Top 14 opener at newly-promoted Oyonnax.
With two hookers out, Toulouse signed recently-retired 36-year-old David Roumieu as injury cover until the end of November.
The former Castres, Bayonne and Biarritz player will make his Toulouse debut against Oyonnax.