St George Illawarra will be without Jason Nightingale for Sunday’s NRL derby clash against Canterbury after the New Zealand winger was ruled out for up to a month with a knee injury.

Nightingale’s leg twisted awkwardly in a tackle in last Friday night’s Test against Australia and staff initially feared the worst when a medicab was called onto the field.

Nightingale got to his feet and played out the match but scans have confirmed medial ligament damage and he’ll be absent for between three and four weeks.

It’s a significant blow to the Dragons backline ahead of the taxing State of Origin period, with fullback Josh Dugan a candidate for NSW duties.

The Dragons are also yet to clear Dugan, Tyson Frizell and Trent Merrin for the Bulldogs clash, after the trio were all late omissions from the NSW Country squad due to minor injuries.

“They did participate in a modified training session on Tuesday, but we will continue to monitor them during the course of this week leading into this weekend’s game,” said Dragons performance director, Andrew Gray.

“(Nightingale) is currently in a brace and we’re expecting him to miss between three to four weeks.”