Celtic could be handed a major Europa League boost after Rennes star Mbaye Niang missed his side's draw with Brest through injury.
Now the former AC milan striker is a major doubt for Thursday's opening Europa League tie against Celtic.
Niang is Rennes' marquee signing this summer after impressing on loan from Torino last season.
And Rennes boss Julien Stephan has confirmed the 24-year-old Senegal international is a major doubt for their opening game against Neil Lennon's men on Thursday.
He said: "Mbaye got a blow to his knee on training this week and that was enough to keep him out of the game.
"As for Celtic, it's just a case of monitoring him on a day-to-day basis to see if he has a chance of being fit for the match this week."
Rennes are already definitely without fellow striker Metehan Guclu, who is out after an ankle operation and central defender Gerzino Nyamsi broke a finger and will be out for two weeks.
Niang, who also had a loan spell at Watford, helped Rennes clinch the French Cup last season and finished as the club's top scorer with 14 goals in all competitions.
