West Midlands Police are set to question Birmingham City defender Stephen Carr over gestures allegedly made to Aston Villa supporters at the end of the Second City derby on Sunday.
Carr had already been facing a Football Association charge over the incident, which came at the end of Birmingham's controversial 1-0 defeat, not only for the events at the final whistle but also for the way he appealed against the award of Villa's winning spot-kick and then scuffed up the penalty spot.
The FA will study referee Martin Atkinson's match report and other evidence before deciding whether to take action themselves, though they will have to wait until the end of any police investigation until they themselves can take any disciplinary action.
City are set to launch their own, internal investigation.
A police spokesman told the Birmingham Mail: "West Midlands Police have received a complaint regarding an offensive gesture allegedly made by a player at the end of the Aston Villa-Birmingham City match on Sunday.
"The matter is currently being investigated by detectives and inquiries are ongoing.''
A Football Association spokesman said: "We are aware of the incident and will be looking at the referee's report and other available evidence before we decide what to do.''