Wellington - Samoa scrumhalf Scott Malolua's Rugby World Cup dream was cruelly dashed on Tuesday when injury ruled him out of the tournament on the same day his team-mates departed for Japan.

The 26-year-old had defied the odds to return from retirement this year and produce a string of performances for the Queensland Reds that earned him an international debut against Australia in Sydney last week.

But Malolua dislocated his shoulder during the 34-15 loss and coach Steve Jackson said he had no choice but to select Pele Cowley as a replacement.

"We're all gutted for Scott, he was playing some good rugby," Jackson said, revealing Malolua was facing eight weeks on the sidelines.

"But we all understand that this is the nature of our game, so we just need to push forward to Japan."

Cowley, from the Ponsonby club in Auckland, was on a skiing holiday with his family in New Zealand's North Island when he learned he was going to Japan.

"It's an unfortunate circumstance in which to be called up, I really feel for Scotty," he said.

"I actually know what it's like because the same thing happened to me in 2015 when I did my AC joint in the last game of the Pacific Nations Cup against Canada, which ruled me out of the World Cup."

Samoa captain Jack Lam took a knock to the eye against the Wallabies but departed for Japan with the team.

The Pacific islanders, who made the World Cup quarter-finals in 1991 and 1995, face Russia in their first match at Kumagaya on September 24.

They will also play Scotland, hosts Japan and Ireland in a tough World Cup Pool A.

Updated Samoa RWC squad:

Forwards (17)

Afaesetiti Amosa, TJ Ioane, Jack Lam, Piula Fa’asalele, Josh Tyrell, Chris Vui, Teofilo Paulo, Kane Leaupepe, Senio Toleafoa, Michael Alaalatoa, Paul Alo-Emile, James Lay, Jordan Lay, Logovi’i Mulipola, Motu Matu’u, Ray Niuia, Seilala Lam

Backs (14)

Ed Fidow, Tim Nanai-Williams, Ahsee Tuala, Belgium Tuatagaloa, Henry Taefu, Alapati Leiua, Reynold Lee-Lo, Kieron Fonotia, AJ Atatimu, Tusi Pisi, Ulupano Seuteni, Dwayne Polotaivao, Melani Matavao, Pele Cowley