The 20-year-old back-rower and utility back Jack Maddocks have joined the Wallabies squad for a clash with Samoa to ease the workload on the World Cup players.

The pair are likely to see game time in the national side's final World Cup dress rehearsal against Samoa at Western Sydney Stadium on Saturday.

The powerful Valetini has been hampered by injury in the early stages of his career but he is still regarded as Australia's next big thing in rugby.

Part of him will always be the 12-year-old schoolchild that wrote "when I grow up I want to play for Australia in rugby" when asked what he wants to achieve.

He will be desperate to make the most of his chance with his family willing him on - not least of which his father Manueli, whose past caught up with him right before he stepped on a Fijian national team bus.

Valetini's call-up comes after he signed a two-year contract extension with Rugby Australia earlier this year which included a Wallabies top-up payment and set him on course for a Test cap.

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He had been a part of the Spring Tour squad as a development player last season but missed World Cup selection this year.

However his looming appearance against Samoa suggests he is still in Michael Cheika's mind heading into a tournament where those left behind have been told to stay ready.

Valetini's call up comes as Wallabies centurion Sekope Kepu prepares to join halfback Will Genia in Test retirement at the conclusion of the Rugby World Cup.

The 33-year-old Kepu, who last year became the first prop to play 100 Tests for Australia, plans to step down from international rugby.

It brings to an end his ties to Australian rugby after quitting the NSW Waratahs to play with UK club London Irish after the global tournament in Japan, which starts later this month.

Kepu is set to farewell fans at the Wallabies' final World Cup warm-up game, against Samoa at Sydney's Bankwest Stadium on Saturday.

"It's going to very special, running out in front of family and friends as well as our home fans for the last time," Kepu said.

The World Cup will be Kepu's third and he feels he's leaving the Wallabies in great shape, with a number of young props jostling for starting positions.

"There's guys pushing for spots everywhere now," Kepu said.

"We have quality depth in Australian rugby and I'll be looking from afar and just excited about what we have.

"We can play anyone in that front row and you can guarantee they are going to do the job, no matter who we are playing."