Neymar gave Brazil cause for concern by hobbling out of a training session less than three weeks before the Copa America starts.
Paris Saint-Germain star Neymar clutched at his left knee after attempting a routine shot and limped away from the session in discomfort.
The injury worry comes less than 24 hours after Brazil boss Tite stripped Neymar of the captaincy and installed Dani Alves as skipper for the Copa America on home soil.
27 year old Neymar spent three months on the sidelines with a foot injury earlier this year.
He returned for PSG towards the end of April and linked up with Tite’s squad over the weekend as Brazil aim to reclaim the continental crown they last won in 2007.
The Selecao meet Qatar and Honduras in friendlies next week ahead of their first Group A game against Bolivia on June 14, with Peru and Venezuela also in Brazil’s group.