Boss Lee Clark has begun his planning for next season by letting the five players leave at the end of their contracts but has offered new deals to Paul Robinson, Jonathan Spector, Wade Elliott, Colin Doyle and Akwasi Asante.
Clark told the club website: "I have pre-warned everybody the last few days that the club is having to go down a completely different route.
"There's no doubting Keith's ability. He is an extremely talented player. But the reasons were mainly financial and a little bit the injuries he has had since I've been here.
"He's not injured now, he's fit, but I have to take everything into careful consideration as we try to move on as a football club, in changing circumstances. Keith has been brilliant.
"He took it really well when we had a chat. He knew the situation we are in and was very philosophical. I would like to thank him for what he has done for this football club and wish him all the very best in the future.
"The same goes to the others - Steven Caldwell, Morgaro Gomis, Pablo Ibanez and Adam Rooney."