Star Wallabies fullback Israel Folau admits he's not sure whether he'll be a rugby union player when the next World Cup rolls around in four years time.

The code-hopping star is off contract in 2018, and will certainly be a player of interest in his old home, the NRL, as well as to rugby union clubs around the world. Folau made his name in rugby league, starring for Melbourne, Brisbane, Queensland and Australia - and he flirted with a comeback, and was on the verge of signing with Parramatta, before talks fell through and he aligned with Wallabies coach Michael Cheika at the Waratahs.

His current three-year deal, signed in July, is a flexible contract which allows him to play stints in Japanese rugby to maximise his earnings - though there are fears over how much of a physical strain it will put on the dynamic 26-year-old's body.

Israel Folau is a two-time John Eales Medal winner © Getty Images

Enlarge

Hopes are high that the Wallabies will be a major threat at the 2019 World Cup in Japan, considering their strong advances under Cheika and the young core of the squad. But losing Folau, the two-time John Eales Medal winner as the best player in Australian rugby, in 2018 would be a major setback to their preparations.

In the wake of Australia's 34-17 loss to New Zealand in the World Cup final on Saturday, Folau was asked if it would spur him on to have another crack in Japan.

"It's hard to say. I don't know what's going to happen in four years time. I am not signed for that long," Folau said. "It hurts now but these are the sort of things you have to put behind you. As I come closer to that point in time to decide whether I want to stay on or not, it is something I will have to consider: whether I have another crack at it."

With or without his talents, Folau believes the future is bright under Cheika.

"My personal view is the team can only get better," he said. "There is a lot of room for improvement with each individual, which obviously means getting better as a collective.

"As a group we take a lot from what has happened in this tournament and take it with us."