Police are investigating chants aimed in the direction of Leicester City supporters by their East Midlands rivals Nottingham Forest.
They are treating the chants as a potential hate crime.
Nottinghamshire Police said it was investigating the “racist” chanting after a video-clip filmed during the club’s FA Cup tie against Leicester was posted online.
The footage, thought to be from the early stages of last Saturday’s 0-0 draw at The City Ground, shows Forest fans singing: “You used to be English, you’re not any more.”
In a statement released by Nottinghamshire Police, Superintendent Mark Holland said: “The incident is being treated as a hate crime and we are reviewing CCTV footage and following up on a number of lines of inquiry.