And, while it is a personal blow for the 10-year veteran, the injury also creates a personnel dilemma for coach Brian McClennan ahead of Friday night's trip across the Tasman to tackle the Tigers.
The club will be crossing their fingers Kevin Locke can recover in time from a bruised sternum, though Auckland Vulcans No 1 Glen Fisiiahi again pressed his claim for an elevation to first grade with another hat-trick in the weekend to take his tally to 18 tries from just eight matches for the feeder club.
Ropati was forced from the field in some discomfort midway through the first half, after an apparent shoulder charge to the head from Roosters' second rower Boyd Cordner resulted in the knee knock.
"That's what's got him and dislocated his knee - coming around the head, when that happens [injuries] can happen quite a bit," McClennan said. "Either you get your knee hurt or your ankle hurt."
Cordner was placed on report for the incident but McClennan bit his tongue when asked how much blame should be apportioned to the Sydney man.
"We've got a system and we'll let that system take care of what happened."
But Roosters' captain Braith Anasta's view of the incident was in stark contrast.
"[The referees] must have watched the Bulldogs game [on Friday night] and just got paranoid about the shoulder hitting the head," he said. "Because it was nowhere near the head."
Regardless of how exactly it happened, Ropati's removal left the Warriors a man down and requiring a reshuffle. James Maloney moved back to fullback and performed capably for the remainder, while Feleti Mateo joined Shaun Johnson in the halves.
Considering the disruption created by key players shifting position, the Warriors did admirably well to overcome deficits on three occasions before surviving a nervy finish to claim the points.
"It's hard when you lose your fullback," McClennan said. "It is difficult for the team when you have to make a change to a pivotal player.
"We just held it together and managed to get some points and hang on."
That was thanks in large to a battling quality that was conspicuous by its absence earlier in the season. After falling into an early 8-0 hole, with thoughts of the 26-8 towelling they suffered at the hands of the Roosters in round five fresh in their minds, the Warriors hit back every time the Roosters seemed to seize momentum.
Doubles from Konrad Hurrell and Shaun Johnson put the home side in charge before Manu Vatuvei appeared to clinch the match with 15 minutes remaining, but the Warriors had to withstand a late onslaught to seal their third win in four games.
