Burnley have asked for an explanation from Ladbrokes after the bookie taunted the Clarets on Twitter.
Ladbrokes are Burnley's official betting partner and even have a stand at Turf Moor named after the brand.
The bookmaker's official Twitter account used offensive messages towards the Premier League club during Tuesday night's Carabao Cup match with Leeds.
The tweets - aimed at former Leeds players Chris Wood and Charlie Taylor - came during the match that the Championship side won on penalties.
Ladbrokes later deleted the tweets but it was too late to avoid the annoying some fans.
Kami Claret tweeted: "Dear Ladbrokes. Account closed. Yours sincerely, Burnley Fan."
A Burnley spokesman told the Press Association: “The club are aware of the problem. We have contacted Ladbrokes and are awaiting a full response.”
Labrokes later apologised for the tweet, telling BBC Sport
"We would like to sincerely apologise to any fans of the club that took offence.
"We have apologised to Burnley FC.
"They (the tweets) were very poorly conceived tweets which we have since deleted. It was only intended to be a bit of fun but failed in that regard."