Paris Saint-Germain coach Laurent Blanc says the injury Zlatan Ibrahimovic suffered in his side's 2-0 win over Bastia was a "strange" one.
The Sweden international appeared to take a knock on his side and had to be substituted after just 15 minutes.
The striker's absence was not felt too much, though, as Lucas Moura and Edinson Cavani steered the champions to a routine victory.
Blanc says a collision was not the cause of Ibrahimovic's injury and instead it was the way he landed which forced him off, adding that he does not know the severity of the injury as of yet.
"At first, I thought he had taken a hit, but no, it was when he turned," the coach told reporters.
"He has a sharp pain in his side. It is a strange injury. I don't know if it is serious, but knowing Ibra, for him not to end the match is something very unusual."
PSG have picked up four points from their first two Ligue 1 matches and face Evian in their next fixture on August 22.