Widely regarded as one of the most exciting young talents to come out of Man United’s academy for years, Gabriel, 15, requested to have his registration torn up.
Man United are yet to respond, but the club have the power to simply say no, meaning the youngster will likely leave next summer instead.
Per BBC Sport, Gabriel is currently in Barcelona to hold talks over a potential move to the Catalan club, although several other top European clubs are interested.
It’s understood that rivals Real Madrid are working on getting a deal done, while PSG and Bayern Munich wait in the wings.
The report adds that the main issue behind Gabriel’s discontent is the club did not register him for their Champions League opener with Sabah FK, which Michael Carrick's side won 4-0.
Carrick spoke about the situation ahead of their Premier League clash with Fulham on Sunday (September 20).
"He's a young boy, JJ, and I think it's important we don't play anything out here," he said.
"With the exposure and scrutiny and everything, you got to be careful and be sensible and think of him as much as anything.
"The situation will work itself out, whatever way it's going to work itself out. Making sure he's OK is the important thing."