The 23-year-old, who missed France’s World Cup campaign with groin damage, suffered a recurrence of the troublesome injury during his side’s humbling 2-1 home defeat by the Romanian side on Thursday.
After the game, Lyon boss Hubert Fournier admitted that Grenier will require surgery in order to prevent further relapses which will keep him out for up to eight weeks.
“We knew he was still fragile. But we played him because we thought he was capable. I am not sure that one more week would have changed anything,” Fournier said.
“He will need an operation, because it is not bearable anymore both for him and for the club.”
Grenier has repeatedly been linked with a move to Premier League side Newcastle United, but Fournier believes that the injury will force his star midfielder to stay at the Stade de Gerland.
He told French reporters: “His transfer? It is currently more likely that he will stay at Lyon.”