Ex-St Kilda coach Grant Thomas has urged his former players not to be content just to get close to rampant AFL powerhouse Geelong in Sunday's qualifying final at the MCG.

Thomas said the Saints had the talent to shock the Cats - winners of 40 of their past 42 matches and hot favourites to win back-to-back flags.

Geelong are rated $1.10 favourites to beat the Saints, who are $6.25 chances with TAB Sportsbet.

But Thomas said the Saints could cause a huge upset, if they were prepared to play demanding, fast football rather than limit the damage from the competition's most brilliant team.

"If Geelong's going to get St Kilda, it'll be through the midfield, but I'm in anticipation of the Saints winning," Thomas told Melbourne radio station SEN on Saturday.

"I just hope they (St Kilda) don't try and get close.

"There's one way to beat Geelong and that's put on unmerciful pressure ... but then have the courage to roll on immediately when you've got the footy and play on instantly.

"If Geelong have time to set up behind the footy, they're just so hard to beat. You won't score."

Thomas's comments came as he revealed he had been able to renew his close relationship with club captain Nick Riewoldt.

Thomas had been a mentor, sounding board and father figure to Riewoldt, but had been warned off by the club at the height of his sacking fallout two years ago.

But the pair have rekindled their friendship in recent months and, coincidence or not, Riewoldt has been in career-best form of late.

Thomas attributes Riewoldt's form to not being as focused on his own performance as he had been in previous seasons.

"Nick is such a high achiever and a driven person that 100 per cent of his focus was on his preparation and his performance, and he delivered on most occasions," Thomas said.

"He's now through maturity got his performance and effort on remote control and now he's been able to open his mind up to his teammates, and provide leadership and direction.

"By Nick bringing other players into the game by being conscious of how his teammates play, it's enhanced him, it's made him a better leader and a player.

"He's in great form and he's on a mission."

Cats premiership defender David Wojcinski has failed to win back his place in the Geelong lineup as he returns from an Achilles injury.

But two other members of last year's grand final team, Andrew Mackie and Max Rooke, have been recalled.

Ryan Gamble and Shannon Byrnes were omitted.

St Kilda have promoted Xavier Clarke and Andrew McQualter to replace Sean Dempster, who seriously injured his knee last weekend, and the axed Shane Birss.