Warm-down sparked fracas

Their decision to ignore requests not to run across the 18-yard box helped spark a mass scuffle between United's players and Chelsea ground staff and stewards.

It is understood players can only warm-down for a total of 15 minutes after a game and they must keep clear of the penalty areas.

Both Chelsea and United have been asked to supply the Football Association with statements relating to the incident and the players and staff involved could face disciplinary action.

United have already sent a report to the FA, but there is unlikely to be an early conclusion to the investigation as both clubs are involved in Champions League games.

In the meantime, the FA continue to seek out all available footage of the incident, which is thought to have been captured by Chelsea's CCTV cameras.

However, earlier allegations the row had been sparked by racist remarks were being played down by both clubs.

It was alleged a racist comment aimed at defender Patrice Evra was at the centre of the fight, which involved more than 20 people.

But a telephone conversation between chief executives Peter Kenyon, currently in India, and his opposite number David Gill forced United to distance themselves from the allegations.

Kenyon is believed to have called Gill the moment he learned United were claiming racist taunts had been the reason for the astonishing bust-up.