Greater Western Sydney have been dealt a big blow in the lead-up to their must-win AFL derby against the Sydney Swans on Saturday, with co-captain and key defender Phil Davis ruled out for the remainder of the season.

Davis strained his hamstring in the second quarter of the away loss to Port Adelaide last Sunday.

He becomes the third Giants star to be ruled out for the season following ruckman Shane Mumford (ankle) and key back Tim Mohr (knee).

On top of that with three rounds remaining and the Giants chasing their first finals berth, star midfielder Dylan Shiel is likely to be sidelined for at least another four weeks with a knee injury.

Davis, who also missed a large chunk of last season with a kidney injury, has played 12 games this year.

He was leading the Giants this season in the so-called ‘one percenters’ – such as smothers, shepherds and spoils.

In better fitness news, midfielders Adam Treloar and Stephen Coniglio will be available for selection this week, while ruckman Rory Lobb (cork) and Lachie Whitfield (concussion) will both be tested.

The Giants must win Saturday’s eighth Sydney derby to have any realistic hope of making a maiden finals appearance.