Birmingham defender Stephen Carr is the subject of a police investigation after allegations he made gestures towards Aston Villa fans at the end of Sunday's derby clash at Villa Park.
And the Football Association have confirmed they are aware of the incident and will study referee Martin Atkinson's match report and other evidence before deciding whether to take action.
Carr and the Blues players were left incensed by the award of a controversial late penalty to Villa which doomed the St Andrew's club to a 1-0 defeat.
Carr was at the centre of the protests and it is alleged he made a gesture towards Villa fans as he left the pitch.
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."
A City spokesman said: "We are aware of the incident and we are looking at it internally."
If the FA decide to take action, 33-year-old Carr, who was persuaded last season to come out of retirement by Birmingham manager Alex McLeish, could face a suspension or a fine.
