Vieira triggered the flare-up when he clashed angrily with United's captain and match-winner.

Keane and Vieira: Non-stop midfield tussle

The Frenchman appeared to butt his opponent as pressure mounted in Sunday's Premiership shoot-out which the champions won 2-1 thanks to two Keane strikes.

A fracas ensued, and Jaap Stam had to be restrained as he approached Vieira - but referee Poll took no action.

Ticking off

The Tring official decided a stern lecture was sufficient as tempers reached boiling point in the fierce atmosphere created by the championship rivals.

"As in every case like this we must first look at the referee's report," said an FA spokesman.

Gunners boss Arsene Wenger claimed he had missed the alleged butt by his star midfielder but may choose to discipline his French international after studying video evidence.

Wenger said: "I will have to look at the tape and see what happened and then maybe decide what action to take."

Keeper crisis

Meanwhile, United are facing an anxious wait to see if keeper Raimond Van Der Gouw recovers from a facial injury picked up at the the end of the fiery Highbury encounter.

United, already without Mark Bosnich due to a hamstring injury, face Lazio in Europe's Super Cup on Friday.