Sydney Swans coach John Longmire is hopeful Josh Kennedy's stint on the sidelines doesn't last any longer than the solitary week after the skipper was ruled out of Friday night's clash with Geelong.

Kennedy, one of four changes for the Round 20 blockbuster at Kardinia Park, was hampered by hamstring tightness during last weekend's contest with Hawthorn with scans later confirming a minor inflammation of the upper leg.

Longmire gave his skipper a 50/50 chance after receiving the better-than-expected news on Monday and held off on making a decision until the team's final training session on Wednesday where Kennedy was given the opportunity to prove his fitness in front of the medical staff and coaches.

But the 29-year-old ultimately succumbed to the tweak, failing to break into convincing strides, and will miss only his fifth game since crossing from the Hawks in 2010.

"I don't know at this stage," Longmire said when pressed on a possible time frame for Kennedy's absence.

"We're hoping it's only the one week ... he was able to run around today but not get to full pace so the risk was too great.

"We'll see how he goes next week."

It will be the second time this season the Sydney Swans will be without their skipper. Kennedy was a late withdrawal from the Round 16 clash with Gold Coast but has otherwise enjoyed a sound season to date averaging 28 disposals across 17 games.

Encouragingly, Longmire has adapted well in despite the contested king's absence having won three of the previous four occasions where Sydney has been Kennedy-less.

However, the coach will need to rely on the likes of Luke Parker and Dan Hannebery to carry most of the load while youngsters Isaac Heeney, George Hewett and Tom Papley step in and help get the job done.

They'll all need to find an extra gear to make up the 15 contested disposals and seven clearances Kennedy has averaged per game in 2017.

Meanwhile, it is also unknown how long big man Sam Naismith will miss as he battles a side strain.

The ruckman failed to train on Thursday and will be another who'll be monitored early next week to determine whether he'll be fit for next week's home game against Fremantle.

Kennedy, Naismith, Jordan Foote (omitted) and Dan Robinson (omitted) were replaced in the Round 20 side by Sam Reid, Kurt Tippett, Jake Lloyd and Gary Rohan.

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