St Kilda coach Ross Lyon says captain Nick Riewoldt could be missing for up to eight weeks with a knee injury.

Key defender Matt Maguire is also set for a significant stint on the sidelines after injuring his foot during Saturday night's three-point win over Richmond at Telstra Dome.

Riewoldt hurt the medial ligament in his left knee when he was thrown to the ground by Richmond defender Luke McGuane early in the second half.

"They haven't graded it fully, he's having scans either today or tomorrow and it's going to be anywhere from three to eight (weeks)," Lyon told Melbourne radio station 3AW.

"If it comes out on the good side it could be three weeks."

Lyon said the Saints had some young key forwards in the wings who were likely to be given a chance in Riewoldt's absence.

"We've got Jarryd Allen who played in the NAB Cup, a tall forward who was an emergency last week," he said.

"We opted for the experience of Fraser (Gehrig) to give him another opportunity.

"We've got young Ben McEvoy, a first round draft pick, really ready to go at 198cm and 98kg."

Lyon said Maguire, who has had a terrible run over the past two seasons with leg and foot fractures, sustained another foot injury on Saturday night.

"We haven't got the full wash-up, but I'm just putting it on the table that it was significant and he'll be out for it looks like a number of weeks, Maguire, and it was his good foot," he said.

"I'm not sure exactly what it is."

The Saints were also hit by hamstring injuries to Max Hudghton and Xavier Clarke, with Hudghton withdrawing from Saturday night's team.

Meanwhile, Lyon said Gehrig's future remained uncertain, with the full-forward having very little impact on Saturday night after being left out of the side for the previous two rounds.

"We'll sit down and assess where he's at," he said.

"Clearly he wouldn't have been thrilled with his performance, but again there wasn't a lot of penetrating ball coming in.

"... I think he looks at (his future), Fraser's very proud and we wouldn't want him to continue playing like he played last night, there's no doubt about that.

"But is it the chicken or the egg? So we'll sit down with him and Fraser will be self-determining, but we'll help guide him where he needs to go."

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