Mendy breaks leg
Mendy suffered the injury while training with the French Under-21 squad and he faces upto six months on the sidelines.
The 21-year-old's injury could also scupper his prospects of landing a permanent switch to The Reebok Stadium.
The pacy full back is on a season-long loan from Paris Saint Germain, with the option of a permanent deal.
But if his lengthy absence is confirmed, Trotters boss Sam Allardyce may be reluctant to gamble on Mendy full time.
Mendy endured a disappointing start to his Bolton career after being plagued by niggling injuries with Allardyce questioning the youngster's attitude to getting fit.
In recent weeks, though, Mendy has established himself in the team and has been a key figure in Bolton climbing off the foot of the Premiership table.
His injury is certainly ill-timed for Bolton, whose threadbare squad will be stretched to breaking point.
Allardyce is furious with the French Under-21s management team and admitted he will demanding compensation for his absence."I'm extremely disappointed and angry with the French officials. He was playing a game not long after featuring in a high-tempo Premiership match," Allardyce told the club's official website.
"This didn't allow him enough time to recuperate and the authorities have not acted in a professional manner.
"Bernard has been playing very well recently and it will be a huge blow to our selection plans for the forthcoming games.
We will be seeking some form of compensation for his absence."