Former All Black great Tana Umaga is to return to New Zealand and leave his post as a member of the backroom staff of France Top 14 club Toulon.

The 36-year-old centre, who was relieved of his duties as player-coach of Toulon after a difficult season in the Top 14 league in France last term, has signed a two-year contract to be the backs coach at Manakau Counties in Auckland.

The departure of Umaga could throw the future of former Canterbury NRL star Sonny Bill Williams into doubt, with the presence of the former All Blacks skipper a main factor in his decision to join the club in 2008.

Williams controversially signed for Toulon after walking out on the Bulldogs midway through the season and has been linked with a return to the NRL and also with Super 14 rugby teams in New Zealand.

Umaga, capped 79 times by the All Blacks, has not ruled out playing again in the New Zealand domestic championship, and is returning home primarily to be with his eldest son Cade, whom he hasn't seen in a year.

"Tana has always been straight, transparent and honest with me and we have excellent relations," said Toulon manager Philippe Saint-Andre.

However, Umaga may even be called upon to play for Toulon before his departure because of a season-ending injury to wing Christian Loamanu and with the club hoping to preserve their place among the top six at the end of the regular season to earn a place in the play-offs.

"I have to be at Counties by the end of June, but if it is necessary to play next week I will do it. Not for 80 minutes mind you, but for at least 20," he told L'Equipe newspaper on Monday.

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