Toulouse's 22-11 victory over Perpignan has come at a cost with Thierry Dusautoir suffering a shoulder injury.
The France captain was forced off in the 44th minute of the win over the defending champions after aggravating a problem in his right shoulder.
Dusautoir had gone into the match with the injury and the move looks to have backfired on Toulouse with the flanker already ruled out the clash with relegation-threatened Bayonne.
"With two young players (Romain Millo-Chluski and Yohan Maestri) in the back row we needed Thierry Dusautoir to give them reassurance despite not being 100 per cent," said coach Guy Noves.
"He is an extremely important part of the squad, but he will no doubt not be fit to play on Sunday against Bayonne. We will see on Thursday if exams are needed."