Dr Tobin told BBC Sport's Dan Roan how Bolton physio Andy Mitchell was the first to spot the player had collapsed.
The doctor recalled: "He screamed, 'Get on the pitch, get on the pitch'. It was obvious something major was happening."
Dr Tobin said Muamba was given two defibrillator shocks on the pitch, one in the players' tunnel and a further 12 in the ambulance on the way to hospital but none worked.
Muamba treatment timeline
Muamba collapses on the pitch due to a cardiac arrest 41 minutes into Bolton's FA Cup quarter-final with Tottenham at White Hart Lane
Medics move Muamba to an ambulance after failing to revive him on the pitch in front of a stunned crowd
Muamba arrives at the London Chest hospital
Muamba receives 15 defibrillator shocks in total before his heart starts beating again
The doctor said it was only when medics at London Chest Hospital took over that the situation began to sink in. He added: "I went into the corridor and cried.
"This is Fabrice, not someone who has gone down in the street. I know him, know his family, joke with him every day."
Tottenham club doctor Shabaaz Mughal was among those who rushed to Muamba's aid. He said: "He appeared to take a couple of gasps but was then unresponsive."
The pair were further helped by Dr Andrew Deaner, Consultant Cardiologist at London Chest Hospital, who was at the game as a fan, and ran on to the pitch to lend his expertise.
He said: "As soon as I saw them start CPR, something twitched in me. You always hope that, if you have a defibrillator and get there quickly, they will respond to at least two or three shocks. The longer the resuscitation, the less the chances of survival. But this is a very fit 23-year-old and those attending him are trained in CPR.
'Miraculous recovery' - Doctor who ran on to pitch speaks to BBC Sport's Dan Roan
"If I was ever going to use the term miraculous it could be used here. He has made a remarkable recovery so far.
"Two hours after [regaining consciousness] I whispered in his ear, 'What's your name?' and he said, 'Fabrice Muamba'. I said, 'I hear you're a really good footballer' and he said, 'I try'. I had a tear in my eye."
The consultant added: "We don't want to get ahead of ourselves but, as things stand, his life is not in danger at this time.
"It is early days so it is not possible to say [if he will play again]."
Dr Sam Mohiddin, the Consultant Cardiologist now looking after Muamba, said: "Fabrice has continued to demonstrate positive signs of recovery.
"His outcome has been extraordinary as a result of extraordinary care.
"He has exceeded our expectations but this remains very early in what could be a very lengthy recovery period.
"The critical thing was the rapid, prompt and very effective CPR at White Hart Lane and expertise from the London ambulance service.
"Normal life is within the spectrum of possibility."
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