Penrith prop Adam Woolnough could be back on the park in less than two months despite initial fears a knee injury suffered in the win over Wests Tigers would end his NRL season.

Panthers officials feared Woolnough had torn his anterior cruciate ligament in Monday night's 30-8 upset of the Tigers, which would require season-ending surgery.

But the Panthers discovered the former Newcastle player had torn his medial ligament and would require only "minor cartilage surgery".

"It's probably an eight week scenario at a maximum and hopefully we can get him back inside that period," Panthers coach Matthew Elliott said.

"But he's a big loss to us for sure."

Penrith also received better-than-expected news on backrower Trent Waterhouse, who is expected to miss three weeks with an ankle injury.

It was initially feared he would miss six weeks.

The club has minor injury concerns over Kiwi backrower Frank Pritchard (ribs) and fullback Rhys Wesser (thigh), but both are expected to be fit to face the Sydney Roosters at CUA Stadium on Saturday night.

"Rhys has got a bit of cork, so there's a little bit of doubt over him and hopefully Franky is right by the end of the week," Elliott said.

Elliott named usual centre or five-eighth Luke Lewis in the backrow in place of Waterhouse, admitting he was reluctant to split up his halves pairing of Maurice Blair and Jarrod Sammut after two straight wins.

Souths-bound Lewis made a successful return off the bench from a finger injury on Monday night with Elliott labelling his impromptu performance in the backrow "something pretty special."

Elliott said confidence was growing at the Panthers but knew his side faced a massive task against the Roosters, fresh from their 40-12 thumping of the Bulldogs.

"We're playing against a side that are in really good form, so it's going to be a huge challenge for us, there's no doubt about that," he said.

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