Lewis Moody is under investigation for wearing a branded mouthguard during the Rugby World Cup quarter-final on Saturday.
The England captain, 33, was reported to the International Rugby Board (IRB) after he was apparently spotted breaching the rules during his side's defeat to France.
"There appears to be a breach of the Team Kit Specifications," an IRB spokesperson told the Daily Mail. "We will be examining the tape of the match and appropriate action will be taken. All the competing sides know the rules surrounding branded mouthguards."
If guilty, Moody will be fined £5,000 for the infringement.
The news is the latest disappointment in England's troubled World Cup campaign. Yesterday Manu Tuilagi was detained by police and fined £3,000 for jumping from a ferry in Auckland Harbour.
