The Football Association is looking into reports of a brawl in the tunnel after Birmingham played Aston Villa.
The FA will study referee Mike Riley's report even though it is believed he missed the incident after the derby.
It will also speak to both clubs, the police and examine footage that could shed more light on a reported fracas between Lee Hendrie and Mario Melchiot.
"We will wait and see what is in the report and look at whether there is any other evidence," said an FA spokesman.
Angry words were exchanged between Villa midfielder Hendrie and Birmingham defender Melchiot at the end of the match.
Stewards came in to defuse the trouble, which lasted for a matter of seconds.
Birmingham boss Steve Bruce said: "I didn't see anything at all - that's all I'm saying".
And a Blues statement added: "An incident is not mentioned in the referee's report and we believe that is the end of the matter."