Barnett has apologised to referee Simon Hooper for the incident during Saturday's 2-0 defeat to Portsmouth, but that has not saved him from an FA charge and he has until 6pm tomorrow to respond.
Barnett's reaction came after he received a second yellow card for conceding a late penalty.
The 25-year-old told the club's website: "I went in straight after the game to the referee and the gaffer to say sorry for my actions.
"I knew immediately that what I did was wrong. What happened was out of character for me and I wanted to apologise for doing what I did."
Source: PA
Source: PA