The New Zealand Warriors welcome back three key players for Sunday's NRL match against the St George Illawarra but have been set back by injury again, with halfback Brett Seymour ruled out for a month.

While loose forward Micheal Luck, half James Maloney and winger Manu Vatuvei return - the latter for his 100th NRL match - the Warriors will be missing Seymour for the match in Auckland after he was diagnosed with a leg fracture.

Only three games into a comeback from a broken thumb, Seymour now faces four weeks on the sideline after scans revealed he has a small fracture at the top of the fibula in his left leg.

Maloney will take Seymour's spot at halfback while Isaac John will make his first NRL appearance of the year, at five-eighth.

John, who played three NRL games last year, has recently returned from a long-term foot injury, featuring for the Auckland Vulcans over the last two weeks.

Seymour left the field with the leg injury early in the second half of Friday's loss to the Wests Tigers in Sydney and it was initially thought he would be clear to play this weekend.

However, Warriors doctor John Mayhew said that would be unwise following the scans.

"It's not of a serious nature. It should heal in an uncomplicated way and won't require surgery," Mayhew said.

"After further assessment from an orthopaedic surgeon today we would expect Brett to be ready to play again in four weeks."

After the Dragons match and an away fixture against Newcastle in the 14th round, the Warriors then have their second bye, meaning Seymour might miss only two matches.

That prospect did little to cheer up Warriors coach Ivan Cleary.

"Everyone knows we've had more than our share of injuries and this is another little setback for Buster (Seymour) who was only just back after missing seven games with his broken thumb," Cleary said.

"At least it's not serious injury and, while we lose Buster, we're helped by welcoming back some serious experience in the shape of Manu and Lucky as well as having Jimmy back from injury."

In his five games this year Vatuvei has scored six tries but has missed the last two matches against South Sydney and Wests Tigers with a leg injury.

"As usual it's an enormous plus to have Manu in the side," Cleary said.

"The fact this match coincides with his 100th in the NRL adds to the day. He really has become one of the game's elite players and it's great to see him reach this mark in front of his home crowd after what he has been through."

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