Lucas Paqueta is being investigated by the Football Association for potential betting rule breaches, sources have confirmed to the BBC.
The West Ham midfielder, 25, has been linked with a move to Manchester City.
On Friday, Paqueta was omitted from Brazil's squad for their upcoming World Cup qualifiers "for him to sort out his problems".
The investigation, which is also said to involve world governing body Fifa, is believed to centre around bets placed in Brazil on yellow cards awarded against Paqueta.
Speaking on Friday, Brazil's interim coach Fernando Diniz said Paqueta had been left out of his squad for qualifiers against Bolivia and Peru next month.