The doctor treating Bolton Wanderers midfielder Fabrice Muamba, cardiologist Dr Sam Mohiddin, has admitted that the cause of the player's cardiac arrest remains unknown.

The 23-year-old collapsed during Bolton's FA Cup quarter-final with Tottenham Hotspur on Saturday and remains in intensive care at the London Chest Hospital.

While Muamba has shown signs of improvement, including the ability to speak in both French and English, Dr Mohiddin has claimed that it is "too early" to pinpoint the cause of his cardiac arrest.

"Almost everybody who comes into us with a cardiac arrest, who has been successfully resuscitated, would be considered for a defibrillator because they're life-saving devices," Dr Mohiddin told BBC Sport. "What has happened may happen again and, therefore, if there's any risk you want a safety net.

"I don't think we can even begin to discuss [whether Muamba will play football again] as it's a question that requires all sorts of unknowns in its answering.

"We believe there are certain conditions that predispose an increased risk of cardiac arrhythmias. Because competitive athletes are stressing their heart in a way that most of us don't, they are probably at higher risk of sudden death."

Meanwhile, the FA Cup quarter-final between Bolton and Spurs, which was abandoned at 1-1, will be replayed on March 27.