Western Force hooker Nathan Charles will miss the rest of the Super Rugby season with a knee injury.

Charles ruptured the anterior cruciate ligament in his right knee during Saturday night’s 19-10 loss to the Cheetahs and is expected to be sidelined for nine months.

The 24-year-old, who is the only known professional rugby player with cystic fibrosis, had been in good form during the early rounds of the season and his absence is a big blow to the Force.

Former Rebels hooker Heath Tessmann is set to be promoted to the run-on side for Sunday’s clash with the Waratahs in Sydney, with Ben Whittaker to be placed on the bench after overcoming a broken foot.

The Force are still sweating on the fitness of injured five-eighth Sias Ebersohn (hip) and prop Pek Cowan (rib).