Mark Nawaqanitawase reportedly will earn $3 million over two seasons with Japan's Saitama Wild Knights.
But Wallabies coach Les Kiss says the 26-year-old must rebuild his 15-a-side game before earning a Test recall.
Nawaqanitawase scored 49 tries in 49 NRL games, including two in the Sydney Roosters' 19-18 grand final win over Newcastle.
His league stint also featured an Ashes series win with Australia and a State of Origin title with NSW.
Speaking ahead of Saturday's Bledisloe Cup match in Sydney, Kiss said Australia had "plenty of good options".
"There's a lot of things and nuances in the game that are quite different (to rugby league)."
Kiss said Nawaqanitawase had not trained for three weeks and should rest before returning to rugby in Japan.
"So he's got a lot of things just to re-learn."
He added: "Won't take him long, that's for sure."
Asked about the 2027 World Cup, Kiss said: "Everyone will earn their way".
He said Nawaqanitawase would be in contention if he played well, adding that selectors would "keep an eye" on him.
Under World Rugby rules, Nawaqanitawase can represent Italy through his grandmother or Fiji through his father from August next year.
Choosing either nation would permanently end his eligibility for Australia.
His agent has said he is considering those options for the 2027 tournament.
Because Nawaqanitawase is not contracted to Rugby Australia or an Australian Super Rugby club, he would receive only match payments if selected for the Wallabies.