Sao Paulo are reportedly demanding that Manchester United pay them a €17m (£15m) instalment that they are owed following Antony's move to Old Trafford within the next couple of weeks.
The 22-year-old followed former Ajax head coach Erik ten Hag to the Theatre of Dreams in the summer transfer window, and his £85.5m switch was made official on deadline day.
Antony made a lightning-fast start to life under Ten Hag at Man United, scoring the opening goal in a 3-1 win over Premier League leaders Arsenal on his debut.
The Brazil international has also started both of Man United's Europa League games so far, and he is under contract with the 20-time English champions until the summer of 2027.
Prior to making the move to Ajax, Antony was a product of Sao Paulo's youth academy, and the Brazilian giants sold him to the Eredivisie champions for a £14.1m fee in 2020.
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As part of the deal, journalist Jorge Nicola - via Sport Witness - claims that Sao Paulo agreed a sell-on clause with Ajax and would receive a hefty chunk of any future transfer fee.
Due to the extortionate nature of the deal, Man United are set to pay the £85.5m transfer fee over the course of five years, but Sao Paulo are pressing to receive their cut imminently.
Nicola states that Rogerio Ceni's side have outstanding image rights payments with their squad, and president Julio Casares promised his players that their monies would arrive following Antony's sale.
Sao Paulo supposedly expected to receive the £15m fee between the end of September and the start of October, but Casares admitted to Nicola that his club are still waiting to be paid.
The Tricolour will take on Ecuadorian side Independiente del Valle in the final of the Copa Sudamericana on October 1, and the report adds that Casares wants Man United to fork out the fee before that game.
Sao Paulo have apparently already received a total of €10.5m (£9.3m) due to their status as Antony's youth club, where the attacker scored four goals and provided six assists in 37 senior appearances.
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Should Man United ultimately be forced to part ways with the cash, their coffers will take another hit before the January transfer window, with Ten Hag and the club's hierarchy said to have differing opinions on mid-season acquisitions.
While the Red Devils manager is keen to add to his squad further, the powers-that-be are allegedly reluctant to sanction any January signings given their significant summer of spending.
Ten Hag has insisted that the January window will be discussed during the international break, though, telling MUTV: "We have many meetings, we have to improve the structures in and around the club, we will do.
"We will also look to the window in January or next summer already but also to improve our way of playing by making plans and, of course, this coming period with every third day a game, we have to get ready for that."
The Red Devils spent big to bring Casemiro, Christian Eriksen, Tyrell Malacia, Lisandro Martinez and Martin Dubravka to the club alongside Antony, but a number of January targets have been mentioned.
Among them is 21-year-old Monaco right-back Vanderson, with a recent report claiming that Man United have entered discussions over a winter move for Antony's fellow Brazilian.
