A depleted Brisbane Roar will face Sydney FC in Wednesday's FFA Cup quarter-final with coach Warren Moon revealing up to six first-team players are unavailable due to COVID-19.

The Roar haven't played since a 1-0 A-League Men defeat to Western United on December 11 due to postponements because of the omicron outbreak.

The effects of the virus and isolation requirements mean Moon will be taking an under-strength squad to NSW for the club's first appearance in the FFA Cup last eight at Netsrata Jubilee Stadium.

"There's just about enough to fill the squad," Moon said.

"We've got boys just coming out of isolation, if not yesterday, then today or a couple of days ago that aren't available for selection because of the protocols and they had symptoms and side effects so they're not 100 per cent feeling great in terms of their fitness, so we can't risk them for tomorrow night.

"There'll be an opportunity for a couple of young boys in the squad to come down and get a game.

"It's not ideal but we're not the only team in this position.

"I know everyone's having to put players in positions where they might not be comfortable.

"Tomorrow we'll see something similar from our boys."

Wednesday's match is also the first of the year for the Sky Blues, with Steve Corica's men last playing in their impressive Boxing Day triumph over Macarthur.

Rhyan Grant, who himself has had to deal with a bout of coronavirus and the after-effects of the illness, said Sydney's players were itching to get back on the park as they continue their quest for a second FFA Cup title.

"It's been a while obviously since we've had the chance to play and I suppose to train as a full squad but everyone's excited, everyone's back training the last few days now," the Socceroos fullback said.

"We've got a full squad ready to go.

"Everyone's just excited to be around each other again and mingling.

"Obviously a pretty important game coming up to which sort of just adds to the excitement."