Patrick van Aanholt was withdrawn from the Sunderland lineup to face Tottenham Hotspur on Sunday after the club were informed of the results of tests on his heart.
Van Aanholt, 26, was due to start the game at White Hart Lane, which Sunderland lost 1-0, but was pulled out half an hour before kickoff. Television pictures showed the Dutch defender reacting with shock when teammate Jason Denayer told him he would be starting in his place.
Sunderland boss David Moyes told his prematch news conference for the EFL Cup game against Queens Park Rangers that the player was stood down on Football Association advice following cardiology tests.