Elvis Vermeulen will be sidelined for four months after being diagnosed with a herniated disc.
Exeter Chiefs will face the Heineken Cup champions for the second successive season after they were drawn with Toulon.
Vern Cotter will remain as Clermont boss for next season before taking up his role as Scotland head coach in June 2014.
Vern Cotter has denied reports that he offered to quit as coach of Clermont to manage Scotland earlier than expected.
Clermont hooker Benjamin Kayser has confirmed he will be fit for France's tour of New Zealand this summer.
Clermont head coach Vern Cotter has confirmed that he will leave the Top 14 outfit at the end of next season.
Castres will face Toulon in the Top 14 Final after claiming a shock 25-9 victory over Clermont in in Nantes.
Clermont are looking to bounce back from Heineken Cup defeat as they take on Castres for a place in the Top 14 final.
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