Tests on Neymar's injured ankle revealed a sprain as well a crack in a bone in his foot, Paris Saint-Germain confirmed on Monday night.
Neymar was injured in the final quarter-hour of PSG's win over Marseille on Sunday, putting in doubt his availability for next week's Champions League second leg against Real Madrid.
PSG did not announce a time frame for Neymar's recovery in confirming the extent of the injury following an ultrasound and CT scans.
"Follow-up exams performed today confirm a sprain in the right ankle, but also the associated presence of a crack of his fifth metatarsal," PSG said in a statement.
Neymar posted a picture on Instagram on Monday morning showing his right ankle strapped and with a protective splint, with the caption "08:10 Finished for today."
PSG also said on Monday that tests on Marquinhos confirmed a "Grade 1" muscle injury in the defender's left quad.
Coach Unai Emery has a regularly scheduled news conference set for Tuesday, during which he could provide more information. After the game on Sunday, Emery said he expected Neymar to be able to play.
He told his postgame news conference: "If I had to pick my Real Madrid side now, I would say that Neymar could feature. The first look says it is a sprain. There will be further tests to be totally sure. We are optimistic."
With PSG already trailing Real Madrid 3-1 after the first leg, Neymar's absence next week would be a huge blow -- particularly when considering they spent €222 million to acquire him last summer in large part to improve their Champions League record.
The French club crashed out in the quarterfinals in four straight seasons before falling to Neymar and Barcelona in the round of 16 a year ago.
Before facing Madrid, PSG host Marseille again on Wednesday, this time in the Coupe de France quarterfinals, and then travel to Troyes in Ligue 1 on Saturday.