Birmingham head coach Pep Clotet has called for "zero tolerance" towards racism after alleging Blues winger Jeremie Bela was abused during Wednesday night's goalless draw at Millwall.
Bela was receiving treatment for an injury 16 minutes into the game when Clotet brought the incident to the attention of the fourth official who informed referee David Webb.
Webb spoke to Millwall manager Gary Rowett before the game continued.
Following the Championship match at The Den, Clotet confirmed he had heard a comment from one fan sat behind the away dugout.
At his pre-match press conference to preview Birmingham's game away at QPR, the Spaniard told the club's Twitter account: "Jeremie is looking forward to helping the team at QPR. He is strong and he will get through this. We need to have a zero tolerance – we cannot accept this."
"It was an individual that said something, it is being investigated, my duty was to report the incident and that is what I did to the fourth official. If I hear something, I will say it. There is no place in football for this. Jeremie Bela is focused."