Tottenham expressed horror at the incident that saw Arsenal goalkeeper Aaron Ramsdale attacked by a spectator at the end of Sunday's north London derby.
The game at Tottenham Hotspur Stadium had just ended when Ramsdale, close to an area containing home fans, was targeted by one supporter who climbed on a pitchside fence and kicked out.
There may be serious repercussions for Tottenham, after security measures failed to prevent the fan getting so close to the England international.
For now, Tottenham have said they are determined to identify the man, who scurried away through the stands after the incident, which was caught by television cameras.
Tottenham said in a statement: "We are appalled by the behaviour of a supporter that attempted to attack Arsenal goalkeeper Aaron Ramsdale at the end of today's match. Violence in any form has no place in football.
"The club has reviewed its CCTV footage to identify the supporter and will be working with the Met Police, Arsenal and Aaron Ramsdale to take the strongest possible action, including an immediate ban from Tottenham Hotspur Stadium."
England's national governing body, the Football Association, said the incident was "wholly unacceptable" and said it would play a full part in an investigation.
It issued a statement that read: "We strongly condemn the incident involving a spectator that followed today's Premier League fixture between Tottenham Hotspur and Arsenal.
"This is wholly unacceptable behaviour and we will work together with the police, the relevant authorities and the clubs to ensure the appropriate action is taken."