’Fearless’ France among World Cup favourites, says Sonny Bill Williams

A "fearless" France are among the Rugby World Cup favourites, former New Zealand star Sonny Bill Williams said ahead of the two teams' heavyweight clash in the opening match of the tournament on Friday.

France and New Zealand have a rich history in the tournament after sharing some classic matches, but the All Blacks have won a record three World Cups while Les Bleus are still searching for a maiden title.

Williams, who won the trophy in 2011 -- when New Zealand edged France in the final -- and again four years later, believes the hosts could peak over the next two months and finally get over the line in the global showpiece.

France have won the last three editions of the under-20 World Cup.

"The last few under-20 World Cups they've won and the young, fearless players that are coming through, France represent that," the 38-year-old Williams told AFP.

"For me they're one of the favourites."

Williams warned the All Blacks to be wary of the threat posed by France's captain Antoine Dupont, even likening the scrum-half to UFC star Khabib Nurmagomedov.

"He's a special player," Williams said. "He's had that 'Khabib upbringing' -- natural physical ability from being in fresh air.

"I like his style, very physical.

"He's a representation of this young scary French player coming through the French system, not scared."

France and New Zealand will expect to reach the quarter-finals even if they lose in the tournament curtain-raiser, with Italy, Uruguay and Namibia making up Pool A.

But the opener offers them a chance to lay down an early marker, with the pair both widely considered title challengers alongside holders South Africa and top-ranked Ireland.

The build-up to the tournament has been overshadowed by a group of former internationals pursuing legal action against World Rugby, England's Rugby Football Union and the Welsh Rugby Union for brain injuries they suffered during their careers.

Williams, who also fought 10 professional boxing bouts, worries rugby union is losing the next generation of players due to the issue.

"We want mothers to believe in our beautiful sport," Williams said.

"There needs to be strategies in place that allow the players to get the best out of themselves by safeguarding themselves and be efficient in that space too... knowledge through science and getting that hands-on approach from people that have actually walked that path."

Williams played as a replacement in both the tense 2011 final win and the 62-13 quarter-final thrashing of France in 2015 as part of an all-conquering All Black side also featuring Richie McCaw, Dan Carter and Ma'a Nonu.

The dual-code international retired from rugby union following New Zealand's surprise semi-final defeat by England four years ago.

"I was lucky, I was very fortunate to be in a great side," Williams, who spent two years of his club career in France with Toulon, said.

"I always loved the fact that I was in a group, in the sheds and I understood there were some great players in the team and all I had to do was my job.

"Some good memories, but everyone has their time."