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"It's a big blow," Lievremont told reporters. "We think he should be absent for two weeks. We will know more in a few days."
Mas was forced to stop training on Friday because of the injury to his right hamstring.
The tighthead started France's 47-21 win over Japan but had not been selected for Sunday's clash against Canada in Napier.
France, twice runners-up, face a key clash against hosts and favourites New Zealand at Eden Park on Sept. 24 before rounding off their Pool A campaign against Tonga a week later.