The 24-year-old hasn't played NRL since coming off the bench for a 48-minute stint in Canberra's 12-10 loss to the Dragons in round 16 on July 3.

After the round 17 bye, Horsburgh didn't feature in the squad for their round 18 trip to Melbourne to face the Storm, but it wasn't until round 19 that he was officially listed with a non-COVID illness.

There was some mystery around the illness, its severity and how long it would keep Horsburgh sidelined, but it has since been revealed just how badly he was affected.

"He had pneumonia and lost about five kilos, but he's back to about 104-105kg now which is his playing weight," Raiders coach Ricky Stuart said on Friday.

Stuart said Horsburgh was now "good" and cleared to return for NSW Cup duties this weekend, starting at lock against the South Sydney Rabbitohs on Saturday afternoon at Canberra Stadium.

The pneumonia infection kept Horsburgh's training to a minimum in recent weeks as he slowly recovered, but Stuart is confident he can work his way back into the NRL side before long.

"It's disappointing for Corey because he was probably in the form of his career and playing with the expectations that we know he could get to [before the illness]," the coach explained.

"It's good to know we're getting him back now, he'll get some good minutes in NSW Cup and get ready for first-grade again."

Ahead of the NRL side's clash with Penrith, Horsburgh's teammate Adam Elliott was also under an injury cloud with a hip complaint. But Stuart said Elliot trained well and "will be right to play".

Our journalists work hard to provide local, up-to-date news to the community. This is how you can continue to access our trusted content: