The Manchester Evening News reports that Gabriel has been keeping fit away from United's Carrington training base by working with coaches in Castelldefels, including private coach Jack Hunter.
The 15-year-old asked United to cancel his contract last month but the club did not agree to his request, leaving his immediate future unresolved as he approaches his 16th birthday.
Gabriel and his family have regularly visited Barcelona, and the Spanish city has become a focus of speculation over his next move. Barcelona and Real Madrid have both been linked with the teenager, although the Catalan club has played down suggestions that it is pursuing him.
Barcelona sporting director Deco addressed the situation at the Portugal Football Summit this week.
“There's nothing to say about this boy,” Deco said. “It's normal that players are linked with us. It always happens. There's a huge market for that with a lot of interests involved, even when [players] are young.
“But we are not interested in any player in his situation. I'm not sure what's happening, and if he's still a Manchester United player. We are not involved in that.
“First of all, we need to understand how the situation is before we try to do something. To speak about young, teenage players, it is not our business.”
Gabriel has not been training with United while the dispute remains unresolved. The Manchester Evening News reported that he had not been at Carrington for more than two weeks and had instead continued his individual work in Spain.
The teenager has been at United since joining the academy at the age of 11 and has developed a significant reputation during his time there. His decision to seek a departure has therefore created an unusual situation for a player who remains contracted to the club.
His 16th birthday is another important date in the situation. Gabriel turns 16 on October 6, with his age relevant to the rules governing transfers and registrations of young players.
For now, however, there has been no confirmed move. Gabriel remains a Manchester United player, is training independently in Barcelona and is waiting for the dispute over his future to be resolved.
The teenager's next club will depend on how that process develops, with United still holding his registration and Barcelona publicly distancing itself from the idea that a deal is currently being pursued.