SYDNEY captain Callum Mills will miss next week's preliminary final at the SCG after suffering a hamstring injury.

Mills tweaked his hamstring at training on Tuesday, the club's first major session since defeating Greater Western Sydey in an epic qualifying final.

Scans on Wednesday confirmed a minor strain for the Academy graduate, who had battled through a bout of gastro to tackle the Giants last Saturday.

The club confirmed the star will miss next Friday's preliminary final at the SCG, where Sydney will host the winner of the Port Adelaide-Hawthorn semi-final.

Mills would be racing the clock to return for the grand final, assuming the Swans advance.

The 27-year-old was also notably plagued by a persistent calf issue earlier this year.

Mills does have some September form when it comes to rapid returns, having injured his hamstring in week one of the 2016 finals then been recalled for the Grand Final that Sydney lost.

Taylor Adams looms as the obvious replacement in the side that rallied from 28 points down to defeat the Giants and earn a week off.

Adams, who left Collingwood to join the Swans in last year's trade period, was dropped in week one of the finals by coach John Longmire.

"His attitude was superb," Longmire said on the weekend.

"I had a chat with him earlier in the week and he's been terrific.

"Who knows what happens in the next few weeks. You got to be on top of you game and all those guys (who didn't play against GWS) will need to be ready to go because that's just the nature of the game."

Mills' setback follows an injury-marred season for the versatile gun.

Mills was sidelined at the start of 2024 after badly injuring his left shoulder in a Mad Monday mishap, having come off second best after wrestling with teammate Jacob Konstanty.

A calf injury then delayed the academy product's return, meaning the final against GWS was just his seventh game of the season.