The Challenge Cup winners accounted for Warrington to launch their play-off campaign last week, but Bradford at Odsal carry a different level of threat, as they showed by winning 49-6 when the clubs met there four weeks ago. Vainikolo scored a Super League record six tries that day. "He was awesome - virtually unstoppable - but we've got to stop the unstoppable," said the Hull coach, John Kear.
Reunited with Shontayne Hape, who agreed a two-year contract extension this week, Vainikolo - "The Volcano" - has once more looked the most dangerous wingman in the game. "I think with his form over the last seven or eight weeks, he's the world's No 1 winger," Kear said.
The responsibility for denying him will fall to Nathan Blacklock, who scored a hat-trick at Warrington last Saturday, but whose defensive qualities will be crucial tonight.
In National League One, Castleford must recover from last week's reverse at Whitehaven if they are to seize their second chance to qualify for their Grand Final.
The Tigers led 18-0 before going down to a 32-22 defeat which their coach, Dave Woods, admits was a major disappointment. "Our players have to lift their game to another plane this time," he said of tomorrow's match against the division's dark horse, Halifax.
Adrian Vowles, who was a substitute last week in his first game back in England, is likely to start for Castleford.
In last season's play-offs, Halifax were close to a defeat by York that would have sent them down to National League Two. A year later, they are within two wins of an unlikely return to Super League, from which they were relegated two years ago. Halifax pulled off a surprise win over Hull KR last week but have five players facing fitness tests before this game.
Castleford could look to the other side of the world for inspiration this weekend, as their namesakes, Wests-Tigers, play the North Queensland Cowboys in the NRL Grand Final. Neither side was expected to get this far; in fact, odds of 300-1 were available for the Tigers a few months ago.
The club, formed by the merger of Western Suburbs and Balmain, has strong English links. Ellery Hanley, Garry Schofield and Lee Crooks, all of whom played for both parent clubs in the 1980s, have sent messages of support.