SYDNEY'S tall stocks have taken another hit with ruckman Sam Naismith in doubt for Sunday's clash against Essendon.

Coach John Longmire has not officially ruled Naismith out, but it would be a cruel blow for the ruckman who has tallied 29 games in seven seasons.

FIXTURE REVEAL New timeslot, primetime crackers, double-headers

"Naismith's a little bit tight in his hamstring, so we will see how the week pans out," Longmire said in his weekly press conference.

Naismith's round one return was one of Sydney's feel-good stories, after the 27-year-old missed all of the previous two seasons with knee injuries.

The news is compounded with fellow ruckman Michael Knoll also set for a longer stint on the sidelines.

"We had a practice hit out on Friday, so Michael Knoll did his PCL which was unfortunate for him, so he'll be out for a few weeks."

The Swans had great success against the Bombers in the ruck department in round 16 last year with  usual defender Aliir Aliir having one of his best games of the season.

Aliir finished with 23 hitouts, eight clearances and 17 disposals as the sole ruckman – a tactic that might work again.

The Swans will also be without forwards Lance Franklin (hamstring), Ben Ronke (knee) and Sam Reid (knee).

Longmire also touched on what will happen with the players who miss out on selection, with scratch matches against the Giants the only real option for the club.

"We're working through that to have a bit of a hit-out with GWS," Longmire said.

"It's imperative that the next group that are coming forward that aren't part of the senior team, still get exposed to some sort of competitive level of football."