Quinton Barham, 13, collapsed on the pitch after complaining of feeling unwell after scoring his third goal.
First aiders and an off-duty paramedic tried to rescuscitate the boy before an air ambulance arrived at the Bromham Social Centre in Bromham, Wiltshire.
Medics then re-started Quinton's heart and he was stabilised before being taken to Bristol Children's Hospital.
His dad Paul, 48, told the local paper: "He is still critical and still asleep, doctors have kept him that way for now.
"He is still on a life support machine and he is undergoing tests to try and find out what is wrong with him.
"We have been told that his pulmonary artery is in the wrong place, it is in the middle of his two heart chambers rather than going through it.
"Because he was playing football and his heart was working hard to pump the blood it basically crushed the artery which caused the heart attack."
Quinton's cousin, Carla Barham, 21, described the teenager, who is the youngest of four, as a 'football mad Man United fanatic' who would do anything for anyone.
Carla, from Melksham, Wiltshire, said: "The whole thing has come as a big shock because he is so young, no one would ever have thought it would happen to him.
"He is just the most genuine kid you will ever meet and if he can't play football again he will be absolutely devastated.
"His whole life is football, if he's not out with his mates playing football then he's in his room playing Fifa, it's all he talks about and all he ever wanted to do.
"He is the biggest Man United fan you will ever meet as well, he absolutely adores them."
Dad Paul, mum Debbie, sisters Toni-Anne and Claire and brother Lathaniel were all at Quinton's bedside as they awaited the results of a heart scan.
Nick Maw, Chairman of Bradford Town Youth Football Club, Quinton's current club, said: "The club's thoughts and prayers are with the boy and his family at this time.
"We are waiting to hear news on the boy's progress but the emergency services were on the scene within minutes and did a fantastic job."