St Kilda and their misfiring AFL attack will be without key forward Josh Bruce for six weeks with a back injury.

Bruce was managing some stiffness in his back when he could not complete Thursday’s training.

Scans showed bone stress and he will be on non-weight bearing fitness work for three weeks.

Bruce had struggled for form in the Saints’ first three games but he was hardly alone.

St Kilda have the AFL’s worst-performed attack and will face Geelong on Sunday off the back of big losses to North Melbourne and Adelaide.

“Your first thought is for the player … (Bruce) had some injuries at GWS, but with us he’s been able to string some footy together,” coach Alan Richardson said.

“He’s become a really important person around our footy club, obviously primarily as a player but also his leadership.

“It’s disappointing not have him there, no doubt.”

The Saints made a big statement by dropping midfielder David Armitage among four changes, while Nathan Wright was left out and Jimmy Webster has a hip injury.

Sam Gilbert, Tom Hickey, Jack Lonie and Jack Steele are the inclusions.

Armitage only managed two games last season because of injury and has not been at his best this year.

“I’ve probably brought him back a little bit too early, I reckon – wanting him to be that player, needing him to be that player,” Richardson said.

“Dave just needs to go back now and get some real run and some real zip in his legs, be aggressive at the contest again – the trademark of his game.

“We need him back in the team, playing really strong, aggressive footy.”

The Cats also made four changes, with Gary Ablett, Nakia Cockatoo and Cam Guthrie injured.

James Parsons was dropped, while Rhys Stanley, Mitch Duncan, Jordan Murdoch and James Cunico have been added.

Richardson said it was crucial the Saints perform better in attack and is optimistic young key forward Paddy McCartin can help lead the way.

“We think Paddy’s been building … the way he’s been able to compete in the air, some of his defensive stuff last week at ground level,” Richardson said of the No.1 draft pick.

“There are some things to like about Paddy’s game but we certainly need Paddy to continue to improve and grow, that’s obvious.

“At our best, we think we can match it with anyone.

“So we’re certainly going down the highway wanting to get our game back.”