St Kilda's chronic shortage of key backmen threatens to further derail the AFL ladder-leader's season.

Having already coughed up ground to its top-four rivals after four losses from the past five games, the Saints must now consider Saturday's round 16 game against Richmond a big danger with four of their best backmen out.

Luke Penny (hamstring) and Matt Maguire (osteitis pubis) were ruled out of the next two games after Sunday's 57-point loss to Melbourne and were joined by Max Hudghton and Troy Schwarze.

Hudghton underwent surgery to mend a fractured ring finger on his right hand, while Schwarze has a hamstring injury.

Both will miss at least the next two games.

With the four - all 190cm or taller - all ruled out, the Tigers only need to stack their forward line with Matthew Richardson and ruckmen Brad Ottens and Greg Stafford in the sanitised conditions of Telstra Dome to create potential match-up chaos for St Kilda.

Leading goalkicker Fraser Gehrig, who played in defence in his days at West Coast, would be option down back for St Kilda coach Grant Thomas, but he still has a game to serve on his suspension.

Similarly, Justin Koschitzke is still sidelined as he recovers from surgery to mend a dislocated elbow.

Making it even tougher for Thomas, his next best defensive option could be Nick Riewoldt, who kicked nine goals against the Demons despite the heavy loss.

The sudden spate of injuries could not have come at a worse time for the Saints, whose form slump means they will be knocked off top spot if they lose to the Tigers.

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