Kantarovksi has a hamstring issue, while Sheppard has a foot complaint.

Both have been officially ruled out of the Jets first game of the season, against Central Coast Mariners on October 19.

"Kanta's hamstring is still very tight," Newcastle coach Ernie Merrick said.

"We are looking at whether the tightness is coming from his back or not. He is going to see Neil Halpin again and we don't want to risk him until we know more.

"Kaine has a foot injury. That was sustained when we received the penalty kick against Sydney, and it's just not right yet. So we've got to do further scans to see what the problem is there and he'll see a specialist.

"They're both definitely out for round one."

New signing Abdiel Arroyo is also recovering from a hamstring strain and Merrick admitted the Jets will need to be careful with the Panamanian in the weeks ahead, after already losing Wes Hoolahan with injury until January.

"Abdiel, against Sydney, sustained a grade one hamstring tear," he said.

"We're just easing him back slowly. We're just easing him back slowly...I'm not sure how much game time he will get on Saturday [against the Young Socceroos] if any. He is not 100% so we have to be very careful with him."

Newcaslte have played nine games in pre-season, six against A-League opposition, and Merrick is pleased with how his team is tracking.

"Even the last game in the FFA Cup, I thought we played really well with 10 men for 80 minutes," he said.

"Where we are fitness wise is good, technically we are good and strategically, I think we have our structures pretty well in place."