Scans on Monday confirmed McInnes suffered a medium-to-high grade medial cruciate ligament injury to his left knee during the final of the NRL nines final.

Fullback option Matt Dufty is all but certain to miss round one after having surgery on a fractured cheekbone that sidelines him for four weeks.

The Dragons did get a slice of good news on Korbin Sims, with X-rays showing no new fractures on a suspected broken arm.

But it is the cruel loss of McInnes that will be most felt by Dragons fans.

Best-case scenario for McInnes would be six weeks, with a return date likely to be whittled down after more follow-ups later this week.

"The specifics of that time frame will be determined by how quickly the ligament tightens up," head of athletic performance Nathan Pickworth said on Tuesday.

"That'll be reassessed later this week.

"Once we have an idea on how quickly his ligament is tightening up, we'll be able to be more specific around his return-to-play time frame."

The development is shattering for McInnes, who was recently appointed to take over from Gareth Widdop as skipper of the merger-club.

It also comes a week after confirmation Jack de Belin's rape trial could be delayed until April, leaving coach Paul McGregor without one of his best players.

McGregor is under immense pressure to get the Dragons off to a strong start in 2020 after his side finished last season in second last spot.

McInnes' absence means the Dragons are likely to rely on veteran Issac Luke for the opening rounds of the competition.

St George Illawarra warm up for the season proper with a trial against Newcastle on Saturday before next week's Charity Shield against South Sydney.

Australian Associated Press