St Kilda’s defensive depth will be tested over the coming weeks with key defenders Sean Dempster and Hugh Goddard joining Sam Fisher in the casualty ward, following Sunday’s loss to Adelaide.

GM of Football Performance Jamie Cox confirmed that Dempster underwent surgery on Tuesday to remove cartilage from his knee, which is expected to sideline the reliable defender for the next month.

The loss of Dempster compounds the Achilles injury suffered by Hugh Goddard against the Crows in the youngster’s first appearance since the final round of last season.

Adding to the carnage in the back half of the ground is the hamstring injury Sam Fisher sustained late in last Thursday’s training session.

“Sean Dempster had a procedure today. He had a bit of cartilage floating around in his knee. So he’s probably four weeks out too,” Cox told reporters at a press conference on Tuesday.

“No Fisher this week, (he’s) probably another two or three weeks away. He’ll hopefully be fit after the bye.

“So we’ll be a couple of keys backs down this week.”

Second-year midfielder Daniel McKenzie was a late withdrawal from Sunday’s game at Adelaide Oval, with the athletic wingman pulling out of the game after waking up with an illness.

Cox said the 2014 second round pick should be available for selection this weekend against Carlton. He was replaced in the selected side by rebounding defender Jimmy Webster.

“McKenzie should be fine. Leading into the morning of the game he was fine, he just woke up a bit ill and was pulled out of the game,” Cox said.

“I guess you’d say with D-Mac if it was a grand final he might have played, but he’s preparation wasn’t perfect so we had someone there to pull in his place.”

With Sandringham in-form and sitting a game outside the top-four on the VFL ladder, Cox indicated that there is a number of replacements ready to step in and make an impact.

“We’re pretty lucky we’ve had a VFL team in really good form and some guys there pushing up hard for a number of weeks so there opportunities will now come,” Cox said.

Key defenders Tom Lee and Luke Delaney should come into the selection frame, with the former travelling to South Australia last weekend as an emergency, along with young midfielder Jack Sinclair.

While Blake Acres, Nathan Wright, Eli Templeton and Lewis Pierce have all been impressive at Sandringham in recent weeks and would be in the mix to face the Blues on Sunday.

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