Neymar had to cut short his first full training session with Brazil ahead of the Copa America after the striker appeared to feel pain in his left knee.
The 27-year-old Neymar left the field in the Granja Comary training ground outside Rio de Janeiro on Tuesday alongside doctor Rodrigo Lasmar.
Brazil's football confederation said Neymar had felt "discomfort" in his knee and was being evaluated by the medical staff.
It was another setback for Brazil's biggest star, who has only played four matches with Paris Saint-Germain since he returned from a broken metatarsal in his right foot on April 27.
That was the same injury that slowed his runs and dribbles at last year's World Cup.
Brazil fitness coach Fabio Mahseredjian had said before the training session that Neymar should be fully recovered after a pair of friendlies against Qatar and Honduras in early June.
But on Tuesday, which marked Brazil's first full training since players started gathering for the South American championship, Neymar had to leave and appeared to be in pain after taking a shot near the end of the session.
The Copa America starts on June 14 with host Brazil facing Bolivia in the opening match at Morumbi Stadium in Sao Paulo. Venezuela and Peru are also in the same group.
Brazil's coaching staff was also optimistic about Neymar's recovery for the World Cup in Russia, but the striker instead made news for his splashy dives rather than his once-frequent dashing performances.
Neymar is also heading into the Copa America, a tournament Brazil hasn't won since 2007, with a disciplinary problem.
Besides being been banned for three matches in France after an altercation with a fan following the French Cup final, Neymar also publicly criticized some of his teammates — a move that Brazil coach Tite doesn't like.
In response, Neymar has been replaced as captain by veteran defender Dani Alves. The Brazilian soccer confederation said Tite made the decision on Saturday after a one-on-one conversation with Neymar.
Cafu, a former Brazil captain who led the team to the World Cup title in 2002, said Neymar was not showing enough respect for the armband.
"Being captain is a big responsibility," Cafu said. "It is more than being the team's star."
Adoration at home has also suffered because of political reasons.
Neymar recently showed support for far-right President Jair Bolsonaro, who has made a series of racist, misogynistic and anti-gay statements.
Weeks later, as Neymar prepared for his return after the injury, Brazilian media reported his father had met Bolsonaro and Economy Minister Paulo Guedes to discuss the player's tax problems.
The Copa America will mark Neymar's fourth tournament played at home. He won the 2013 Confederations Cup and the gold medal at the 2016 Rio de Janeiro Olympics, but his team was eliminated in the semifinals of the 2014 World Cup. Neymar was injured and didn't play in the 7-1 loss to Germans.
