The Socceroos star, who recently returned to Australia when he joined the Victory, has entered into a sponsorship agreement with Ford - a direct competitor to FFA sponsor Hyundai, which lends its name to the national competition.
Kewell's agent Bernie Mandic has informed Buckley that it was unlikely to stop there with the ex-Leeds United, Liverpool and Galatasaray star looking to get involved with some other lucrative sponsorship deals.
''I have been informed by Bernie Mandic that Harry has and is contemplating entering into arrangements with competitors of our major sponsors,'' Buckley said.
''It's vital that the integrity of our commercial partners is maintained for the benefit of all players in the competition and the benefit of all clubs and the game more broadly.''
Buckley said that what Kewell has done does not align with the standard player contract (SPC) he has signed and revealed the FFA would monitor his dealings very closely.
"There is provision in the collective bargaining agreement to recognise legitimate pre-existing agreements,'' Buckley added.
''But if agreements are entered into since the agreement to play for the club was made and the formalities of completing SPC have not been completed I would question the legitimacy of that approach.
''We will be reviewing this (Ford agreement) very closely.''