Clermont number eight Fritz Lee is extremely doubtful for their Champions Cup semi-final against Saracens due to a hamstring injury.
The powerful back-row came off in the second-half of the 37-5 win over Northampton, having played a key role in setting up Clermont's first try.
However after undergoing tests on Tuesday, it was revealed that he is suffering from a hamstring strain, and is very unlikely to return for the semi-final in a fortnight.
"The MRI that Fritz Lee underwent this morning showed muscle damage in his right hamstring," read a statement from the club.
"It's a similar injury to that suffered by Wesley Fofana in the last few weeks. It's a blow for the number eight who is now out of the weekend's game with Oyonnax and is extremely doubtful for the semi-final between Clermont Auvergne and English side Saracens in a fortnight in Saint-Etienne."