GREATER Western Sydney has been dealt a massive blow with running defender Zac Williams facing a month on the sidelines with a hamstring injury.

Williams let the field in the third quarter of Friday night's win over Collingwood and failed to return.

The Giants had initially hoped it was just a tweak, but subsequent scans revealed more damage.

"He had a little grab in his hamstring when he kicked the ball off the ground early in that third quarter," Giants head of medical Cullan Ball said.

"We got a scan on his hamstring which just shows a little split in his upper hamstring tendon. We think Zac will probably miss about a month."

In better news for the Giants, key defender Phil Davis is a chance to take on Hawthorn this week despite also failing to finish the match against the Pies.

"Phil just felt a little bit of tightness in his hamstring and we decided not to take any risks with him," Ball said.

"He's had a scan done which came up really well for us. That's clear and he’ll be a test for this week's game and fingers crossed he’ll be all good."

Meanwhile, Isaac Cumming will miss up to three months after a significant hamstring injury in the reserves practice match.

Reigning club champion Tim Taranto is expected to return within the next month from his shoulder reconstruction.