The 22-year-old former Wests Tigers custodian will start at the back against Manly at EnergyAustralia Stadium on Monday night because an ankle injury to regular pivot Ben Rogers has forced Stone to switch captain Kurt Gidley to the halves to partner Jarrod Mullen.

McDonnell has become accustomed to biding his time behind Gidley since joining the Knights from the Tigers midway through last season.

But Rogers is at long odds to return this year and if McDonnell plays well against the Sea Eagles, Stone intends keeping him there and leaving Gidley at halfback.

Rogers was injured in Newcastle's 28-24 extra-time loss to the Cowboys in Townsville last Saturday and has been diagnosed with lateral ligament damage and a small impaction fracture in his left ankle, which is expected to sideline him for four to six weeks.

"I've spoken to Shannon about it and at the end of the day, he picks himself," Stone said. "If he's playing really well enough, I'll find a place for him in the team there somewhere."

McDonnell appeared in eight of the first 12 matches this season but has not played since Newcastle's 28-10 loss to the Panthers on June 5, when he ran for a game-high 151 metres.

Rather than feel frustrated about being left out of the 17-man NRL squad for the past seven weeks, McDonnell said he had kept working hard to be ready when opportunity knocked.

"You can't do anything about it. It's out of your control so the only real thing that can benefit you is to put your head down and arse up, train hard and keep yourself fit for when the opportunity arises," McDonnell said.

"It all comes down to playing well, so if I do that whatever happens happens."

A broken thumb, knee cartilage damage and rib cartilage damage have contributed to his stints on the sidelines but McDonnell said he was 100 per cent fit and ready to go against the Sea Eagles.