GREATER Western Sydney's tilt at a first finals campaign has been dealt a serious blow with the news that ruckman Shane Mumford will miss the rest of the season with an ankle injury.

Arguably the club's most important player, Mumford will have ankle reconstruction surgery this week, after suffering the injury in the Giants' 42-point loss to Collingwood on Sunday.

Scans have revealed that the 28 year-old tore the deltoid ligament in his left ankle.

WATCH: Four Giants struck down with injury against Magpies

The club's number two ruckman Adam Tomlinson is already in the rehab room with a toe injury, so Mumford's replacement is likely to be 11-gamer Andrew Phillips, who has made one appearance in 2015.

Coach Leon Cameron concedes the loss of the reigning club champion will hurt the Giants, but says Mumford's absence will give an opportunity to the club's younger players.

"It's a good test for our young group, some kids have been playing some good footy in the NEAFL, so it's a good challenge for us," Cameron said on Tuesday.

"You don't like losing key position players and leaders of your footy club, but that's life.

"The good thing about Mummy is there's a smile on his face, he's disappointed he's going to miss footy, but what he's looking forward to is helping (Andrew) Phillips, and (Tom) Downie) and young Rory Lobb take their opportunity.

The news doesn't get any better for the Giants, with co-captain Phil Davis also to be out of action for six to eight weeks, who also suffered an ankle injury against the Pies.

Davis sprained ligaments in his right ankle just before half time at the MCG on Sunday, and will join fellow key defender Joel Patfull in the medical room.

Patfull punctured a lung and broke two ribs in an accidental collision with teammate Matt Buntine, and will miss the next six to eight weeks of footy.

The Giants' key defensive jobs will now fall to 23 year-old Nick Haynes and 22 year-old Aidan Corr, who have played a combined 59 AFL games.

Haynes (192 centimetres and 87 kilos), plus Corr (195 and 88) will be fighting out of their weight divisions against the like of Drew Petrie, Jarrad Waite and Ben Brown when the Giants face North Melbourne this week.

While undersized, Cameron has faith in his pair of youngsters to get the job done.

"I can't sit here and predict what's going to happen, all I can say is that I'm very, very confident that our young group will rally, and fight and find a way to play a very competitive brand," Cameron said.

"That’s the confidence I have, starting with Saturday.

"Aidan Corr played particularly well in the NEAFL on the weekend so we look forward to him coming back into the team and making a stance, and saying 'look I can play key position', and I think he's looking forward to it as well."

Many have written off the Giants' finals hopes after the fallout from the Collingwood game was revealed, but when asked if his side's top eight chances have disappeared, Cameron said his focus hasn't changed.

"Even before these guys became injured I never ever looked too far, it's a week to week prospect for us," Cameron said.

"We're not in a position to actually state that we're a finals team yet. I stated at the start of the year that it would be disappointing if we didn't make finals within the next two years," Cameron said.

"Have we improved this year? Absolutely. Are we in a good position? Yes we are, at the half way mark of the year.

"Do I expect us to win more games? Yep, and do I expect a really competitive performance and (us to) take it up to the Kangaroos on Saturday? I expect that to happen, and I'm confident it will happen.

In a slightly better outcome for GWS, midfielder Stephen Coniglio's shoulder injury isn't as serious as first thought, and although he's likely to be sidelined for three weeks with a grade two AC joint injury, with the Giants' bye he may only miss two games.