St Kilda is set to risk injured full forward Fraser Gehrig and has elevated Justin Koschitzke to stand-in skipper for its AFL match against struggling Carlton on Sunday.

Gehrig, who has a ruptured thumb ligament, was named in the Saints side and will wear a protective guard on his hand after training strongly.

And 22-year-old Koschitzke has been given the job of captaining the Saints in the absence of injured skipper Nick Riewoldt, who is set to miss up to six weeks with a broken collarbone.

Saints coach Grant Thomas said Riewoldt had recommended Koschitzke be anointed as his replacement, starting with Sunday's match at Telstra Dome.

"He's very proud and honoured to have the title of captain, but he's in the leadership group and it's all about leadership," Thomas said.

"He's a very competitive person.

"He instills a lot of confidence and determination in his teammates and it will be a great learning curve for him."

Gehrig was expected to face immediate surgery on the injury sustained in his side's win over the Western Bulldogs last weekend.

Instead he will try to play through the season with the injury, though he is certain to have to go under the knife at year's end.

"It's just a matter of how much he's inconvenienced - it will need an operation and that will probably be done at the end of the year," Thomas said.

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