Newcastle have been dealt a blow with leading A-League marksman Roy O'Donovan ruled out for three to four weeks with a groin injury.

Goalkeeper Jack Duncan is also out of second-placed Newcastle's home match on Thursday night against Melbourne Victory.

Irish striker Donovan, who has scored seven times in his first season with the Jets, had been a late withdrawal from Saturday's away loss to Sydney.

Scans have revealed he has a grade-one tear to his adductor.

"He will miss at least the next two games against the two Melbourne clubs with a groin injury," Jets coach Ernie Merrick said.

"Roy's a professional of the highest order and takes really good care of himself.

"He's also a real competitor and I know he won't like to be missing games, so he'll be doing everything he can to get this right and return to the starting XI.

"In saying that, we certainly won't be rushing him back, it's a long season ahead and we'd rather have Roy unavailable for a few weeks now than a large portion of the rest of the season."

Duncan, who has started every game this season, has a foot injury and will be replaced on Thursday by New Zealand international Glen Moss.

"We're not sure of the extent of the injury just yet," Merrick said. "Jack will be having further scans and seeing a specialist later this week.

New Newcastle Jets recruit Roy O'Donovan has scored seven goals from six A-League appearances this season. Ashley Feder/Getty Images

"Glen Moss will come into the starting XI. We've got great depth in our keeping stocks, with Ivan Necevski continuing on the bench."

O'Donovan's place as central striker will again be filled by wide man and former Victory player Andrew Nabbout, who had occupied the spot against Sydney.

"It was okay. I've played there a few times when I was coming up with Victory and in the last couple of seasons," Nabbout said.

"I'm comfortable there; it's a bit different; you have to be a little more patient."