Sonny Bill Williams' much-anticipated return as Toronto's $10 million man is set to be delayed as the former All Black makes a rushed trip back to New Zealand for the birth of his fourth child.

Williams had been included in the Wolfpack's 21-man squad for Monday's (NZ time) trial match against the Castleford Tigers, but with his wife, Alana Raffie, about to give birth to the couples' fourth child, Wolfpack chairman Bob Hunter confirmed to the Sun-Herald that Williams would be heading back to New Zealand.

"We're just trying to arrange his airline ticket now," Hunter told the Sun-Herald. "He needs to get back for the birth of his child, so we'll give him a few days. I think February 2 will be his first game."

Hunter was pleased with Williams' impact on and off the training field, saying there has been much more interest in the club since his arrival, although he won't be playing on Canadian soil until April.

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"The significance of Sonny's personal brand has been wonderful," Hunter told the Sun-Herald. "On both sides of the pond, it has been very positive.

"I'd say sponsorship has increased about 25 to 30 percent, and our season ticket sales are up at least 30 percent from last year. But one of the problems is we play our first 10 games in the UK, so it's tough to get that excitement building in Toronto."

The Wolfpack return to Canadian soil for the second half of the competition when the local weather improves.

Meanwhile, the Wolfpack confirmed Williams will wear the number 21 on his back for the 2020 season.

In June 2018, Williams became a father for a third time when their first son, Zaid Williams was born. The name Zaid is of Muslim origin and translates to "to prosper".

The pair are already parents to daughters Aisha and Imman.

Williams has not played rugby league since the 2014 NRL season with the Sydney Roosters but there is already intense interest about whether Williams will play in the 2021 World Cup - and for which country. Williams will be 36 when the tournament starts.