St Kilda captain Nick Riewoldt has confirmed he will be out of AFL action for at least 12 weeks with his hamstring tendon injury.

The Saints had been careful not to put a timeframe on the recovery period for their most important player, only expressing confidence he would return in the latter part of the season.

St Kilda and Riewoldt are very confident he will be ready for the finals.

Riewoldt needed surgery on Monday to repair a hamstring tendon after he tore it just before halftime in last Friday night's win over Collingwood.

"Probably 12 (weeks) is something like the minimum for this sort of injury, but again they haven't had too much experience with this particular type of injury," Riewoldt said on Channel Seven's The Bounce.

"It's not a tendon off the bone, as some people were reporting, or a tendon off a muscle junction, it's a pure tendon injury."

His absence will mean a massive challenge for the Saints, but Riewoldt has faith they will be able to reorganise their attack and remain competitive.

St Kilda narrowly lost an epic grand final to Geelong last year and have started this season with three-straight wins.

Before his successful operation, there was plenty of speculation about how long Riewoldt would be sidelined - including fears that the injury might end his season.

Riewoldt admitted he was nervous before receiving the good news that the surgery had gone well.

"It's pretty nerve-wracking, to be honest, when I did it originally," he said.

"I haven't had much experience with hamstring (injuries) ... so I didn't know what to expect.

"There were a lot of doomsdayers, I suppose, who were saying `off the bone', and then some were saying regulation four to six (weeks).

"So I just threw my arms up in the air and really was willing to accept whatever happened, providing I could get back later in the year, which is the case."

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