Johnnie Matthews, 36, said the decision to jump into the water - which was only a few feet deep - wasn't "his cleverest idea".
He has had a season ticket since 2015, despite living in Farborough, Hampshire.
Johnnie travelled to watch the Brentford match in the away end with around 1,800 other fans.
However, he was to make a huge call to friends.
"I made a comment to the lads, if Leeds stay up, I’m in the Thames", Johnnie said.
"We’d just left the ground and walked down the river to a pub, there was a bit of goading going on but as I’m not a good swimmer, I said I’d find somewhere to jump in where I know I can get back out, it looked deep from the bank but turns out it wasn’t.
"I knew as soon as I hit the bottom I was in trouble, getting back out was a real challenge not being able to stand.
"I’ve damaged both of my feet, left is just bruising and cuts, and I’ve shattered my right heel."
Johnnie is now awaiting a call from the hospital to see if he requires surgery.
He has been left unable to "walk or work".