Liverpool forward Ryan Babel has been fined £10,000 and warned about his future conduct for posting comments and a doctored picture of Howard Webb on Twitter.
The Holland international was charged with improper conduct by the Football Association after he used the social networking site to criticise the official.
After the Reds' FA Cup exit at Manchester United, where Liverpool conceded a controversial first-minute penalty and had captain Steven Gerrard sent off, Babel posed a mocked-up picture of Webb wearing a United shirt.
He also wrote: "And they call him one of the best referees? That's a joke. SMH (shaking my head)."
Babel later apologised for his comments and posted: "My apology if they take my posted pic seriously. This is just an emotional reaction after losing an important game.
"Sorry Howard Webb."
At a regulatory commission hearing the 24-year-old was fined £10,000 and warned as to his future conduct.
In summing up, the regulatory commission chairman Roger Burden said: "Social network sites, like Twitter, must be regarded as being in the public domain.
"All participants need to be aware, in the same way as if making a public statement in other forms of media, that any comments would be transmitted to a wider audience.
"It is their responsibility to ensure only appropriate comments are used."
Speaking today, shortly before Babel's punishment was announced, Professional Footballers' Association chief executive Gordon Taylor told Sky Sports News: "Players have got to be mindful that it's only like doing a nationwide television interview or having an article in a national newspaper.
"They've got to me mindful of what they say and make sure that it's in the rules of the game and not bringing the game into disrepute."
Taylor insisted banter was all part of the game but added: "If it does go over the top then there's a need for a warning to try to make sure that it doesn't happen again.
"But just try to keep a sense of proportion on things."