Mr Hirst, 28, last year became the first rugby league player to come out as gay while playing professionally.
In a statement on its website the club said that the fan had been “using homophobic abuse” on social media.
It reads: “There is no place in our sport for homophobic abuse or indeed any abuse and we wish to send out a clear message that if you engage in such behaviour we do not want you to attend our stadium.”
It also states: “Since Keegan publicly confirmed his sexual orientation we have been delighted by the response and support he has been given by everybody at the Club and indeed throughout our sport.
“This is the first and hopefully the last time we witness such unpleasantness.”
Mr Hirst’s friend Mr Cotton, who plays Sean Tully in Coronation Street, is a supporter and regular visitor to the club.
The decision to release a statement was praised by Mr Hirst on Twitter.
He will soon leave the Bulldogs to play for Wakefield Trinity Wildcats.