Patrick van Aanholt was withdrawn from the Sunderland lineup to face Tottenham Hotspur on Sunday after the club were informed of the results of tests on his heart.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. The player has now been given the all-clear and could feature at Loftus Road.
Moyes said: "He had the statutory checks with the cardiologists and the FA panel of cardiologists looked at it and advised us really late on Sunday that he should not play until further tests had taken place.
"We are just surprised that the FA panel didn't contact me or contact my doctor until 3:55 p.m. on Sunday afternoon. I have never in my career been put in a situation like that ever, so we had that to deal with.
"We just can't understand why the message would come to us at that time, 30 minutes before the kick-off."
However, the FA, which carries out around 1,400 screens across England and Wales each year, has insisted it had no formal involvement in the matter.
A spokesperson said: "This cardiac screen was not conducted as part of the FA's cardiac screening programme, therefore the FA had no involvement in the player's referral, the screening process or the communication of the results with the club.
"On occasion, clubs may seek independent advice on a player's cardiac health from an expert cardiologist who sits on the FA Consensus Panel, which is an expert body in this area.
"Cardiologists who sit on the FA Consensus Panel are hugely respected and vastly experienced specialists who place the patient at the very centre of their care and their only concern will be in regard to the well-being of that individual.''
Moyes will be without Victor Anichebe and Jermain Defoe as he rings the changes for Wednesday's tie at QPR. They will also be without the suspended Adnan Januzaj, who was sent off after receiving two yellow cards at Spurs.
He said: "Jermain took a bit of an injury in the game [vs. Tottenham], he's got a knock so he won't go and more importantly I need to make sure he's fit for the game at the weekend.
"Victor isn't ready to play yet but he's stepped up his training and he's getting much closer to match fitness."
"There will be some young boys involved but we've already had players such as Duncan Watmore, Lynden Gooch and Jordan Pickford play well.
"We have a young team so the addition of players like Lee Cattermole, Jan Kirchhoff and Steven Pienaar has given us more experience, but we've had a young side for most of the season and it will be the same tomorrow evening."