New Vodafone Warriors halfback Brett Seymour has been sidelined for at least six weeks after breaking his left thumb in his debut appearance for the club against Gold Coast last Sunday.

The 25-year-old Seymour believes the injury happened early in the second half of the match.

Vodafone Warriors doctor John Mayhew said it would be at least six weeks before the playmaker would be able to return to the field.

Coach Ivan Cleary said the injury was a big disappointment for both Seymour and the club.

"Brett had done so much work to get himself ready," he said.

"He played in all the trials and really impressed in those as well as the game against the Titans. We're all disappointed for him."

With Seymour ruled out, fellow off-season recruit James Maloney will now move in to fill the halfback's role against Cronulla in tonight's second-round NRL clash at Mount Smart Stadium with Joel Moon coming off a five-man bench to start at standoff.