A video posted on social media appears to show a policeman push an MK Dons fan to the floor in The Drapery before Saturday's match with Northampton Town.
Police took part in high-visibility patrols in Northampton town centre ahead of the two sides' meeting at Sixfields Stadium, where an increased police presence was in place.
In the video, police can be seen segregating a group of fans to the left of the Game shop on The Drapery, from another group seen walking towards the bus station.
A man - believed to be an MK Dons supporter - can be seen walking up to a police officer who then pushes the supporter with both hands, resulting in the fan falling back on to the road.
Northamptonshire Police said they are looking into the matter.