Bolton midfielder Fabrice Muamba has announced his retirement from football.
Muamba, 24, collapsed and suffered a cardiac arrest on 17 March during Bolton's FA Cup quarter-final tie with Tottenham Hotspur.
"While the news is devastating, I have much to be thankful for," Muamba told the club website.
"I thank God that I am alive and I pay tribute once again to the members of the medical team who never gave up on me."
Muamba had travelled to Belgium earlier in the week to have minor heart surgery, which was said to have been routine and had no bearing on whether the player would return to action.
But Muamba says he received advice during his time there, prompting his retirement.
"Since suffering my heart attack and being discharged from hospital, I have remained utterly positive in the belief I could one day resume my playing career and play for Bolton Wanderers once again," said Muamba in a statement.
"As part of my ongoing recovery, last week I travelled to Belgium to seek further medical advice from a leading cardiologist.
"But the news I received was obviously not what I had hoped it would be and it means I am now announcing my retirement from professional football."
The news comes just six months after he suffered his cardiac arrest, with doctors saying he was "in effect dead" for 78 minutes.
He was given 15 defibrillator shocks before his heart started beating again, taking 48 minutes between collapsing and reaching the London Chest Hospital, and a further 30 minutes once at the hospital.
Muamba then spent around four weeks in intensive care, before being discharged from hospital on 16 April.
He then returned to the Reebok Stadium before Bolton's match with Tottenham on 2 May, to thank the Bolton supporters.
Muamba began his career at Arsenal and moved to Birmingham City, before spending four years at Bolton.
"Football has been my life since I was a teenage boy and it has given me so many opportunities," he said.
"Above all else, I love the game and count myself very lucky to have been able to play at the highest level."
Bolton manager Owen Coyle - who chatted with Muamba just three days after the midfielder's collapse - paid tribute to him and said the club will support him.
"We have spoken with Fab and he knows we will always support him in whatever he wants to do and that we will always be here for him," said Coyle.
"He is obviously massively disappointed that he won't be able to carry on his career, but everyone has seen what a fighter and strong person he is in mind and body.
"We know that he will go on to achieve great things and within all this disappointment, the most important thing is that he is here, alive, today."
Bolton chairman Phil Gartside also said he was simply thankful for Muamba being alive.
He said: "To have Fabrice here and with us is truly amazing and we are all very thankful for that.
"The most important thing is that Fabrice and his family have the rest of their lives ahead of them."
Fifa president Sepp Blatter wrote on Twitter: "Have just read about your retirement. It's very sad for you and I wish you all the very best."
Football Association chairman David Bernstein was also among the well-wishers, saying: "His recovery has been miraculous and a great tribute to all who have been involved.
"I would like to wish him the very best for the future and I know that the thoughts of the entire football family will be with him."