Paris Saint-Germain superstar picked up an adductor injury in the 2-0 win away at Istanbul Basaksehir in Champions League Group H and requires scans to ascertain the extent of the damage.
The Brazil international was replaced by Pablo Sarabia after 26 minutes in Turkey after signalling to coach Thomas Tuchel that he needed to be withdrawn.
Neymar, 28, is now without a goal in five Champions League appearances and had his first two seasons in France disrupted by metatarsal problems.
"He needed to come out," Tuchel said post-match. "It was necessary. Now, we must wait. Neymar was not in real pain, but he felt uncomfortable. With our tight schedule, it can cost him multiple games. However, I am unsure at this moment.
"I hope it is not serious," he added to RMC Sport. "We need to wait and see the scan results. It is his adductor."
Neymar is likely to miss this weekend's trip to Nantes in Ligue 1 and depending on the severity of the injury, could also miss next week's Champions League clash with RB Leipzig and the approaching international break.
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Brazil are due to face Venezuela and Uruguay in World Cup qualifiers with Barcelona's Philippe Coutinho already out.