Holders Paris Saint-Germain reached the last 32 of the French Cup with a 1-0 win at Ligue 2 side Caen on Wednesday, but striker Neymar suffered a possible thigh injury six days before their Champions League last-16 first leg against Barcelona.
Moise Kean scored the only goal early in the second half before Neymar limped off the pitch just after the hour, raising concerns about his participation in the Camp Nou clash.
"There's something with his adductor [muscle]. It will be checked by the medical staff tomorrow," PSG coach Mauricio Pochettino told a news conference.
"We don't know what it is, we'll know more tomorrow. We can't say anything before he's been examined tomorrow."
With Kylian Mbappe and Marquinhos on the bench, PSG struggled against a compact Caen side.
Neymar found himself isolated and the French champions failed to create a clear chance in a dull opening half.
Yet the visitors sprung to life after the break as Kean netted from close range from Neymar's cross at the end of a counter attack four minutes into the second half.
Neymar, however, went down after a robust challenge from Steeve Yago in the 56th minute, holding his left thigh as he left the field to be replaced by Mbappe.
PSG will already be without the injured Angel Di Maria for the Barcelona game.