Hull KR captain Terry Campese has been ruled out for the rest of the season after rupturing his anterior cruciate ligament.
The 30-year-old half-back suffered the injury in his side's defeat by Castleford earlier this month.
He scored two tries in 15 Super League appearances after joining from NRL side Canberra Raiders last December.
"It's very disappointing to lose Terry for such an extended period," coach Chris Chester told the club website.
"He has really settled into the Super League competition and was playing some fantastic rugby for us, so to be without him for the rest of the season is tough to take.
"We've been unlucky with injuries this season, but we've never tried to hide behind that as an excuse and it's important now that we don't feel sorry for ourselves. "
Hull KR are 10th in the Super League table, with seven wins from their 17 games so far.