Melbourne's NRL finals stars aligned with their gun five-eighth Gareth Widdop a late starter against Newcastle.

Widdop was believed to be no chance of playing against the Knights in their qualifying final after injuring his ankle in the final-round game against the Roosters.

However, Widdop made a miraculous recovery through the week, with coach Craig Bellamy even more thankful when his choice to replace the 22-year-old, Rory Kostjasyn, limped offAAMI Park in the warm-up with a hamstring problem.

Maurice Blair, who was named in the match-day program at five-eighth, was ruled out on Thursday - also with a hamstring injury.

Bellamy said after the match if he hadn't given Widdop the green light to play, he would have had to have started his skipper, hooker Cameron Smith, in the No.6 jersey.

"We thought he (Widdop) was out for two or three weeks and the scan reinforced that on Monday," Bellamy said.

"The physio said on Wednesday he's not really feeling much pain and was a chance to play.

"He trained a full session on Saturday but I still wasn't sure if I was going to play him."

Bellamy said Widdop - who was a fullback until this year, when he was crafted into a five-eighth, following the departure of Brett Finch - won him over.

"It wasn't just how he trained physically but he had plenty of talk and he looked like he was up for the full session.

"I thought he did a good job so it was probably a good move."

Kostjasyn will undergo scans on his hamstring, with Bellamy concerned he might have some nerve damage.

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