Millwall defender Alan Dunne has been hit with a £2,000 fine from the Football Association following comments made on Twitter.
The 29-year-old used the social networking site to re-tweet a critical comment about referee Jon Moss.
Full-back Dunne was sent off during Millwall's 6-0 defeat to Birmingham City last month and went on to post the comment criticising the referee's decision.
Dunne, who has been with the club since 2000 after joining at eight years of age, admitted to the FA's charge of improper conduct and requested a personal hearing on the matter.
The Irishman was also warned about his future conduct as a number of footballers and other sports people continue to find trouble following comments made on Twitter.
Following the disciplinary hearing, Millwall manager Kenny Jackett has issued a warning to his players but insists they will not be banned from using the website.