The veteran, who has been with the club since 2007, is not getting a new deal.
It appears the midfielder's time with the Championship side is nearing its conclusion.
The man who arrived from Sheffield Wednesday more than a decade ago has only played nine games this term.
"It has been the honour of my career to have played for this great football club for the last 13 years but today I must begin saying goodbye," said Brunt in a statement.
"Before I go any further, I should make it clear that my entire focus over the next few weeks will be on doing everything in my power to get us back to the Premier League, to where this club and its fans belong.
"Though it may not come as a massive surprise to many, I thought it best we clarify the situation now, before we begin playing the final nine games of the season. We cannot afford to have any distractions from our goal."