Rapana is unlikely to suit up for the Raiders in their top four showdown against the South Sydney Rabbitohs at Canberra Stadium on Saturday.

The 29-year-old went for scans on Monday after injuring his knee during Canberra's defeat at the hands of the Sydney Roosters over the weekend.

Club officials are hoping for good news but expect he is unlikely to play this week following what early indications suggest may be a posterior cruciate ligament injury.

It means Canberra could be forced to field a makeshift right edge featuring Bailey Simonsson and Michael Oldfield given Joey Leilua's season is likely to be over.

Rapana is off-contract at the end of the season and the Raiders are keen to keep one of the competition's most destructive wingers in the capital.

He will play a key role in Canberra's bid to return to the finals as the club sweats on the results of the scans which could play a defining role in how far they go this year.

The New Zealand international has endured a frustrating start to the season on the injury front but has still managed to feature in seven of nine games.

Rapana himself says "it's not terrible" considering he was not even supposed to return from a shoulder injury until last weekend. However he has been hit by a rib issue and now a knee problem to rob him of consistent game time.

His absence would give Simonsson a chance to return to the starting side against the high-flying Rabbitohs this weekend after he came from the bench last weekend to replace Rapana.

"It's lucky we had Bails there on the bench [against the Roosters] I guess, but it would have been nice to use him differently," Raiders captain Jarrod Croker said.

"If we just kept Rapa on the edge and had Bails floating around that middle with some tired players would have been nice."

Rapana's absence would force Canberra to field a makeshift right edge with Oldfield already drafted in as cover for star centre Leilua.

Neck surgery may well bring down the curtain on Leilua's season and Rapana's latest injury would be a cruel blow for a Canberra side that has made such a promising start.

But Croker maintains the Raiders will be able to plug the gap with Oldfield following his return against the Roosters.

"He handled it quite well out there, a lot of their attack went towards them a little bit and I think Oldy handled himself quite well," Croker said.

"It's hard to get a gauge from where on how all the structure is but it seemed to be good from where I was."

Rapana joins an overflowing injury ward at Raiders headquarters with John Bateman (fractured eye socket), Joe Tapine (ankle), and Luke Bateman (knee) all sidelined.

Canberra coach Ricky Stuart says if the Raiders can keep scrapping and pick up a few wins they will be well placed to launch a raid on the finals come the back end of the season.

While he would love to have a full-strength side every week, Stuart says the absence of some key players can prove to be a double-edged sword because "we're getting a lot of experience for young players".