ST KILDA'S worst fears for Jake Carlisle have been realised, with the star defender set to have back surgery later this week which could ruin his entire season.

A disc protrusion in his lower back was causing pressure on a nerve, with the operation set to relieve that.

He will be extremely limited for the six weeks after going under the knife, upon which time he will be in rehab for several months.

The 27-year-old has managed a back issue for several seasons, but it has proved particularly problematic during this preparation.

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His back showed signs of improvement on various occasions but setbacks always followed.

"When he's playing well, we know Jake is one of the best defenders in the game, so it's obviously disappointing not to have him available," football manager Simon Lethlean told saints.com.au.

"Given he hasn't been able to train with any intensity since Christmas, we were able to prepare for the start of the season knowing he would likely be missing, but unfortunately he will now miss a considerable amount of football.

"Guys like Josh Battle and Darragh Joyce have stepped up over the summer and will get their opportunity, which is exciting.

"Thankfully with Dylan Roberton back, joined by the likes of Jarryn Geary, Jimmy Webster and Nathan Brown, we have good experience in our backline that will be able to help fill the void."

He missed five games in 2018 – one in the week his son Nash was born, which meant Carlisle couldn't prepare as he needed to, another because of concussion, while a punctured lung forced him to miss an additional match.

The former Bomber was also banned for two games after striking Richmond spearhead Jack Riewoldt.

His marking prowess will be sorely missed in defence.

Making matters worse, Brown will be unavailable for round one against Gold Coast while he serves the final match of his suspension for a heavy bump on Essendon speedster Adam Saad late last year.

Promising young backman Oscar Clavarino won't be available to debut for more than a month as he deals with a right ankle syndesmosis issue.