Manchester City midfielder Joey Barton has been fined six weeks' wages, two of which are suspended for a year, after an incident at their Christmas party.
The 22-year-old poked a cigar in the eye of team-mate Jamie Tandy after he was said to have provoked him by trying to set his shirt on fire.
Tandy was fined two weeks' wages, which was suspended for a year, and found guilty of misconduct.
The incident happened at a Manchester nightclub on Sunday.
City chairman John Wardle said: "We have been let down badly.
"The events of Sunday evening fell seriously below the high standards we expect and demand at this football club.
"They were totally out of order and completely unacceptable.
"I have never had to deal with anything of this severity. I hope I never will again and have made that perfectly clear.
"All the players are fully aware of the disciplinary standards we expect at this club.
"The manager outlined them at the start of the season - as he does every year. That is why we have come down so strongly on this matter.
"Our players know the rewards their job brings them but they must also realise the responsibilities that they have to this club, our supporters and our community should be a lot higher than they are. I hope they accept that."
Police did not investigate the incident but Tandy did receive hospital treatment for burns on his eyelid.
Barton's future at the club has been called into question before.
He has been in trouble for on-the-field misdemeanours, with Keegan recently warning him to improve his behaviour.
Barton, who was not present when his punishment was announced, has apologised for his actions at Sunday's Christmas party.
He said in a statement: "I
feel embarrassed about what I did and deeply regret it.
"I fully accept the punishment and have co-operated fully with the disciplinary proceedure."