The 63-Test Wallaby is understood to have died on Saturday night. It is believed there were no suspicious circumstances. Vickerman leaves behind a wife, Sarah, and two young children.

Vickerman, 37, was a South African-born second rower for the Wallabies between 2002 and 2011 and played his professional career with the Waratahs and Brumbies.

After playing in his second Rugby World Cup in 2007, he took a break from from international rugby for three years to study in England. He earned a degree in Land Economics from Cambridge University and also had a short stint with Premiership club, Northampton Saints in the 2009-2010 season.

He was forced to retire in 2012 due to persistent injuries to his leg, and went on to carve out a career in commercial real estate.

Australian Rugby Union chief executive Bill Pulver has expressed his condolences, saying Vickerman was a well-loved figure amongst rugby circles.

"The rugby world is in shock today after news of the tragic passing of Dan Vickerman," Pulver said in a statement. "Dan was an uncompromising competitor who forged a wonderful international rugby career despite a number of injury setbacks along the way.

"He was an enforcer on the field and a much-loved character off the field. He cared deeply about the game and the players, helping players transition into life after rugby in his role with RUPA following his retirement.

"Our thoughts and prayers are with Dan's family at this extremely difficult time."

Phil Waugh, a close friend of Vickerman's and a teammate at Sydney University, NSW and Australia, said it was a terrible day for rugby in Australia.

"We all have huge admiration for the guy that he was," Waugh said. "He was one of those players when you're standing next to him in the change room and he's running out next to you, you had so much confidence. He's a guy that necessarily wasn't the loudest in the team, but had the most respect from everyone playing with him. There's so many positive memories of him on and off the field.

"He was an uncompromising competitor. Nothing came easy to him and he worked hard for what he got out of the game. He was a very good friend of mine and we caught up frequently and it's a huge loss to all of us.

"Everyone's deeply shocked and saddened by it. It's just a terrible, terrible tragedy that has rocked everyone."

Another former Wallabies teammate, Matt Burke - who was unaware of the news when contacted - could not speak highly enough of the man who played 53 matches in the sky blue jersey.

"Very abrasive as a player but a good bloke, though," Burke said. "Great lad, great tourist, a very good player who came across from South Africa as a young bloke, played Waratahs, played Brumbies, played Wallabies. He could really play and was just one of the good lads that you enjoyed his company."

Former Wallaby legend Simon Poidevin said in a text message: "Absolute tragedy, we are all in shock".

Jeremy Paul, who featured in 72 Tests for the Wallabies, paid tribute to Vickerman.

"He had such a life to live with his wife Sarah and their two young kids," Paul told Fox Sports News. "All our hearts and well wishes go to Sarah and the two little kids.

"It's a bit of a shock. He actually came out and did some work for me in regards to Penrith when I was coaching the Shute Shield and we've always tried to catch up Billy Young's pub with all the boys and have a get-together like the good old days."

Waratahs chief executive Andrew Hore said: "Dan was well respected for his on field leadership and performance and equally respected by all that knew him off the field.

"His tireless commitment and passion to helping improve rugby as well as his commitment to supporting players throughout their careers through his role with RUPA, is a legacy that will long live on.

"The shockwaves of his tragic passing will be felt right across our rugby community.  Our thoughts are with his wife Sarah, their two sons and other friends and family during this difficult time."

Rugby Union Players' Association chief executive Ross Xenos said: "On behalf of all players, we extend our deepest sympathies to Dan's young family at this difficult time. We are truly shocked and united in our despair.

"Dan was universally respected by his peers and the rugby community during and beyond his playing days. Since retiring, he was very generous in giving back to the game through coaching and voluntary roles supporting players' off-field development.

"We encourage all players who are affected by today's terribly sad news to support and be there for each other and to contact RUPA if they would like to talk."

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