Liverpool forward Ryan Babel has been charged with improper conduct by the Football Association for posting a picture of Rotherham referee Howard Webb on Twitter.
The Holland international sent out a mocked-up picture of the 2010 World Cup and Champions League final official wearing a Manchester United shirt following his side's 1-0 FA Cup third-round defeat at Old Trafford.
Babel also wrote: "And they call him one of the best referees? That's a joke. SMH (shaking my head)."
The 24-year-old later added: "My apology if they take my posted pic seriously. This is just an emotional reaction after losing an important game.
"Sorry Howard Webb."
The apology has not been enough to prevent a charge from the FA, who said in a statement: "The charge relates to comments and images published by the player on Twitter concerning referee Howard Webb."
Babel has until 4pm on Thursday to respond to the charge.
Liverpool manager Kenny Dalglish said earlier he felt it was just a joke and had hoped further action would not have been necessary.
"Maybe I've been out of the game too long but let's see if they can find a sense of humour," he said.
"He apologised straight away."
And Dalglish joked: "I don't think he's clever enough technically to have drawn that up himself."
The FA are also thought to be looking into events during the FA Cup third-round tie between Blackburn and QPR.
Rovers' 1-0 win at Ewood Park on Saturday was overshadowed by the broken leg suffered by Rangers striker Jamie Mackie in a tackle with Gael Givet.
While he was lying injured, Mackie was reportedly taunted by Blackburn striker El-Hadji Diouf, leading QPR boss Neil Warnock to call the Senegal international the "lowest of the low" and a "nasty little person".
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