South Yorkshire Police have launched an appeal to find witnesses to the alleged tunnel incident at Oakwell involving Fleetwood Town boss Joey Barton and Barnsley counterpart Daniel Stendel.
Stendel reportedly needed emergency dental treatment in the wake of the Tykes’ 4-2 win on Saturday.
Both clubs are assisting with the police investigation, while Barnsley have also lodged a formal complaint with the EFL and the FA.
A South Yorkshire Police statement said: "Police investigating reports of an assault at Barnsley Football Club on Saturday 13 April are appealing for witnesses as enquiries continue.
"The incident is believed to have taken place in the tunnel around 5pm, following the conclusion of Barnsley's match against Fleetwood Town, and left one man with facial injuries.
"At this time, no arrests have been made in connection with the incident."
Officers are particularly interested in hearing from anyone who may have captured a confrontation between the men following the Yorkshire club's 4-2 League One win on camera.
The statement continued: "Were you at the game on Saturday with a view, or in the area, of the tunnel? Did you see what happened?
"Officers are particularly keen to speak to anyone who may have caught the incident on camera or who may have any mobile phone footage immediately before or after the incident occurred.
"If you think you can help, please call 101 quoting incident number 326 of 13 April 2019."