21kg shed in 18 months: Will Skelton sacrifices World Cup for Saracens

Former Wallabies second rower Will Skelton has finalised what he's described as the toughest decision of his playing career.

The 27-year-old is expected to sign a two-year contract extension with Premiership club Saracens on the eve of their monumental Champions Cup final against Leinster this weekend in a deal that will rule him out of contention for this year's World Cup in Japan.

Despite some late persuasion from Wallabies coach Michael Cheika, who is looking to bolster his stocks in the underperforming lock department, Skelton is set to extend his stay in London with the club that has helped him shed 21 of his 140kg in 18 months, propelling him into career-best form.

Starring in an all-star squad that features internationals such as Maro Itoje, Owen Farrell, the Vunipola brothers, Schalk Burger and Liam Williams, Skelton falls well short of the required 60 test caps to be eligible for Wallabies selection while playing overseas, with just 18 tests to his name.

"I had some chats with Cheik at the start of the year and my manager has spoken to him a lot," he told AAP.

He was trying to get me back home and there were some [Super Rugby] offers but it is difficult because I've agreed to stay here.

"There's still a few bits and pieces to nut down but I am close to signing a new deal here.

"It was a massively difficult decision given the World Cup is this year but if the rules change in the future I'll always put my hand up to play for Australia."

Skelton's rise to prominence at Saracens hasn't come easily, however.

Head coach Mark McCall warned his star man upon his arrival at the club in 2017 that he'd never fulfil the potential that he showed when he debuted with the Waratahs at the age of 19 unless he lost some weight.

"Will's been a revelation since he came over here," McCall told AAP.

"But he'll be the first to admit he's been a bit a slow burner.

"He's always been a huge talent and able to bring something to a team that other players can't, not only because of his size but his skill set as well. But what we needed from Will was for him to have a bigger impact in games and the only way to do that was for him to lose some weight.

"He's done that through his own single-mindedness.

"The club love him, the coaches love him and the players love him, and we want to keep him."

After helping steer Saracens to their fourth-ever Premiership crown last season, Skelton's side look on track to at least seriously challenge for back-to-back titles, but before then, a European showdown with Leinster awaits in Newcastle on Saturday.

Saracens won the last of their two Champions Cups in 2017, and standing in their way of claiming their third European title in four seasons is Leinster forward and Skelton's former Australian teammate Scott Fardy.

"Fards' always tough, he is a great player and great bloke, as well," he said. "He's gone over there and added value to Leinster and help make them successful.

"It will be a great challenge and I am looking forward to it - these are the games every rugby player wants to play in."

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