Neymar was forced off with a nasty left knee injury during Brazil's 2-0 defeat to Uruguay in a World Cup 2026 qualifier.
He sustained the injury after tripping and falling during a run in the 44th minute, shortly after Darwin Nunez had given Uruguay the lead at the Centenario Stadium.
The 31-year-old received treatment for several minutes and was reduced to tears as he was taken off on a stretcher.
He is now set to undergo further tests but is potentially a doubt for Al-Hilal's much-anticipated AFC Champions League match against Mumbai City FC in Mumbai.
"Let's hope it's nothing serious," Brazil captain Casemiro told Globo television.
"He's an important player for us, we're very fond of him. He's been suffering a lot from injuries and when he starts to pick up the pace he gets injured again."
The defeat means Brazil are third in South American qualifying after suffering their first defeat in a World Cup qualifier since 2015.