Muamba, the Bolton Wanderers midfielder, fell to the ground suddenly - 41 minutes into the game against Tottenham Hotspur, at White Hart Lane, which was on live television.
No other players were near him at the time.
The match was abandoned as both teams’ doctors spent ten minutes treating him on the pitch in front of around 35,000 fans.
Muamba, 23, was taken to the Heart Attack Centre at the London Chest Hospital. In a statement, his club said he is in a critically ill condition in intensive care.
Reporters at the game said he was not breathing as he was stretchered off the pitch and into an ambulance.
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Wishing him speedy recovery!