Arsenal captain William Gallas' kick out at Manchester United winger Nani last month is again under scrutiny.

The Mail on Sunday says the FA are investigating referee Alan Wiley's refusal to punish Gallas for kicking out at Nani during Manchester United's FA Cup-tie against Arsenal at Old Trafford.

Gallas appeared to kick the back of Nani's legs after becoming aggravated by the young Portuguese star juggling the ball beyond the reach of Arsenal's defenders.

Wiley did not book Gallas on the day and FA officials are baffled that he has not since issued a retrospective red card.