South African prop Jannie Du Plessis is set for a month on the sidelines with a hamstring injury, his French Top 14 club Montpellier said on Tuesday.
The 34-year-old former Springbok international was injured during Montpellier's 16-3 defeat at Lyon on Saturday, being forced off inside the opening half hour.
Du Plessis's injury is another headache for Montpellier, who already have Georgian prop Davit Kubriashvili out until April with a calf problem.
Australian international full-back Jesse Mogg will be rested for a week after taking a knock to the head against Lyon that saw him forced off the field for a head trauma assessment.
However, there is better news for Montpellier as Fiji wing Nemani Nadolo, who was knocked out against Castres at the end of January, is set to make his return for the trip to Clermont.
Montpellier sit fourth in the Top 14 with Clermont second.