Chemistry graduate Wetherall, who scored the goal that secured City's Premiership safety against Liverpool in May 2000, moved across West Yorkshire from Elland Road for £1.4m in 1999.
Howard Wilkinson signed him for Leeds from Sheffield Wednesday in the summer of 1991 and he played over 200 league games for the Whites.
A boyhood Leeds fan, Wetherall had a playing contract with Bradford until 2010, but with a clause inserted into the deal to allow him to end his playing days when he saw fit.
Wetherall, a virtual ever-present this term, said: "I was just beginning to feel frustrated with the things I can't do anymore that I used to be able to do. Certainly next season that would only increase.
"I'm not one of those people who can kid themselves they can go on forever, you can't. I want to look back and be able to say yes, I did my best and did the best with what I had."