ST KILDA midfielder Koby Stevens has announced his immediate retirement from AFL football, after an ongoing battle with concussion.

Stevens, 27, informed his teammates of his decision on Monday afternoon.

The midfielder has been plagued by concussion symptoms, suffered when he clashed heads with Brisbane Lions midfielder Mitch Robinson in Round 1.

Stevens played out the Saints’ Round 2 game against North Melbourne, before making the decision to speak with the St Kilda medical staff after feeling “really ill”.

Stevens told Fox Footy’s On The Mark in May that the incident made it hard for him to concentrate for more than 10 to 15 minutes.

“It’s a day-to-day thing. Some days I wake up and I’m pretty clear and then I try do a little bit of exercise and as soon as my heartrate gets up, I just get real chronic headache and pretty dizzy.” Stevens said.

The midfielder played 91 AFL games for West Coast, Western Bulldogs and St Kilda over a nine-year career, averaging 18.4 disposals and 3.9 tackles.

“This decision has taken me a long time to come to,” Stevens told the club’s website.

“Football has been a huge part of my life for as long as I can remember, and I do recognise how lucky I have been to play professionally for the past nine years.

“However, after lengthy consultations with my family and on the advice of doctors, I’ve made the extremely hard decision that I cannot risk my health and future for the game.

“I’m so grateful for the support of the entire St Kilda Football Club, particularly the medical and player development staff who have been extremely supportive of me over the past few months.

“To my teammates and coaches, both here at the Saints and at my previous clubs, thank you for allowing me to live my dream. I can’t thank you enough for all that you’ve done.

“Lastly, to my friends and family I couldn’t have done this without you.”

Stevens suffered multiple concussions during his footy career, but he said none were more confronting than the one he experienced after clashing with Melbourne’s Angus Brayshaw in Round 21 last year.

“I reckon that one was the worst one I’ve ever had,” Stevens said on Fox Footy’s On The Mark.

“I wasn’t knocked out, but it felt like a bomb had gone off. I couldn’t hear anything and it hit me right in the ear drum, so for about 10 to 15 minutes I had ringing in my ears.