Lyon striker Lisandro Lopez is out for a month after suffering a blow in the 2-1 home victory against leaders Montpellier on Saturday.
Lopez was stretched off in tears at the end of the match with a serious left ankle injury and the prognosis was not good on Monday.
"The Argentine striker will have a cast for 10 days. He will be out of action for at least four weeks", Lyon said on their official website.
The striker was recalled by Argentina's new coach Alejandro Sabella after a long absence and will miss the friendly games against Venezuela in Calcutta on Friday and Nigeria in Dhaka four days later.
He is also certain to miss Lyon's Champions League Group D opener at Ajax Amsterdam, while he will be a serious doubt for the second leg against Dinamo Zagreb.