The Football Association have confirmed that they will investigate Gary Neville's behaviour during Tuesday's Carling Cup semi-final first leg at Eastlands between Manchester City and Manchester United.
Former United star Carlos Tevez scored both City's goals as Roberto Mancini's team hit back from a goal down to win the tie 2-1.
The Argentina international appeared to gesture towards Neville, who was warming up on the touchline, after scoring his side's equaliser from the penalty spot, with the United veteran responding with what appeared to be a one-finger insult of his own.
The FA confirmed on Wednesday morning that they were 'looking into' the incident, which was caught on camera.
Tevez found the net 34 times in 99 appearances during his two-season loan spell at Old Trafford, but United boss Sir Alex Ferguson baulked at the fee he was asked to pay to make the 25-year-old's move permanent last summer and he was eventually snapped up by City.
Ryan Giggs had given United a 17th-minute lead at Eastlands but, after Tevez had equalised from the penalty spot, the Argentinian headed home City's dramatic second-half winner.