THE PLAYING future of St Kilda's Jake Carlisle has been placed in doubt after the veteran was sent for back surgery on Friday which is expected to sideline him for the remainder of the season. 

The 29-year-old hasn't been seen at AFL or VFL level since leaving the training track with a back complaint during the main session ahead of round seven with a decision made to operate this week. 

It is the second time in three seasons Carlisle's season has been impacted by back surgery after he missed the first half of the 2019 season when he was put under the knife in February. 

Carlisle was forced to wait until November last year to win a one-year contract for 2021 after being in and out of the Saints' best line-up during 2020. 

He played four games from rounds three to six this season as a relief ruckman due to an injury to Rowan Marshall and Paddy Ryder working back from personal leave. 

"We've been working with Jake on treatment plans, however his level of day-to-day pain and restriction of movement has gotten to a point where lumbar disc surgery is the best option," Saints chief operating officer Simon Lethlean said. 

"The delicate nature of spinal injuries means is pretty hard to put a timeline on recovery.

"Our doctors and physios will work with Jake throughout his rehab, and we'll monitor his progress. 

"While it's a disappointing outcome, Jake's long-term health and overall wellbeing is paramount."

The Saints moved to add key defensive stocks this season, selecting mature-age prospect Tom Highmore in the draft and pulling Hawthorn premiership full-back James Frawley out of retirement. 

Prior to Carlisle's setback, the Saints had the option of using four picks in the NAB AFL Mid-Season Rookie Draft after leaving one spot open following the Pre-Season Supplemental Period (SSP), to go with openings due to Dylan Roberton's retirement and season-ending injuries to Ben Paton and Jade Gresham.  

Carlisle has played 151 AFL games – 85 for Essendon from 2010-2015 and 66 for the Saints from 2017.