Arsenal defender Gabriel is in a race to prove his fitness ahead of Brazil's World Cup clash with Haiti.
The centre-back played the full 90 minutes as his nation began their campaign with a 1-1 draw against Morocco.
Gabriel was well off his best in that match, getting caught out of position for Morocco's opener and looking shaky throughout the match.
There is now uncertainty over his involvement on Saturday night when Brazil attempt to pick up their first win of the tournament against Haiti.
Gabriel is understood to have missed training on Wednesday due to discomfort in his left adductor.
He did some light work away from the main group along with Raphinha, who has been managing blisters.
It is unclear how serious Gabriel's issue is, but reports in the Brazilian media suggest that Carlo Ancelotti is still hopeful that the centre-back will be available against Haiti.
Gabriel will continue to be assessed and particular attention is being paid to his fitness after such a heavy workload this season.
The defender played more than 4,000 minutes across 51 matches for Arsenal in all competitions and was one of their most consistent performers in the Premier League title-winning campaign.
Gabriel picked up an thigh issue in November while on international duty and missed six weeks of action, but was otherwise an ever-present for the Gunners.
With Raphinha not involved in training for Brazil on Wednesday, Gabriel's club team-mate Gabriel Martinelli is said to have been more involved in first-team preparations.
The winger did not get any minutes in Brazil's opener against Morocco but is pushing to play some part on Saturday night in Philadelphia.
