The FA is to investigate the incident in which Sheffield Wednesday goalkeeper Chris Kirkland was attacked during a match by an opposing fan, English soccer's ruling body said on Saturday.
Kirkland, a former England international, was knocked to the floor with a push to the face by a Leeds United supporter during an English Championship (second tier) game on Friday.
"We are investigating the events of last night and awaiting the referee's report," an FA spokesman said.
The 31-year-old Kirkland received medical treatment on the pitch and was able to finish the Yorkshire derby which ended in a 1-1 draw.
"With the public's assistance we have clearly identified the offender who ran onto the pitch during last night's game... and who is suspected of assaulting the Sheffield Wednesday goalkeeper," said South Yorkshire Police's senior investigating officer Detective Inspector Mark Monteiro.
"We are dealing with the complaint made by the player and we are currently taking statements, collating evidence and making enquiries to locate and arrest the offender.
"We are also using CCTV footage from around the ground to identify suspects who may have been responsible for other offences before, during or after the match."
Wednesday manager Dave Jones and his Leeds counterpart Neil Warnock, in television interviews after the match, called for tough punishments, including stadium bans and jail terms, to be handed out by the authorities.
Kirkland told Wednesday's official website (www.swfc.co.uk): "I was looking at the ground but when I looked up, I caught a glimpse of someone coming towards me on the pitch.
"I thought he was going to give me some abuse but then suddenly he came at me with both hands and I was stunned.
"I felt the full force and I was just shocked because you never know what could have been in his hands...
"I just want the authorities to look at what happened and take the appropriate action because sooner or later, we could be talking about something even more serious".
Leeds issued a statement on their website (www.leedsunited.com) condemning the supporter involved in the incident.
"Leeds United Football Club would like to publicly apologise for and condemn the actions of the fan who came on to the pitch at Hillsborough and attacked Sheffield Wednesday goalkeeper Chris Kirkland," Leeds said.