A shattered Vaea has been ruled out of the entire ACT Brumbies' season before a game has been played and he is using blood-thinning medication to help him overcome his condition.

A clot formed on Vaea's heart last year and bits started to break off and were found in his kidneys and calf at pre-season training.

It's a blow for the powerful 24-year-old, who was starting to establish himself as one of the hardest hitters and most devastating runners in the competition.

But coach Jake White says the ''Brumbies family'' will rally around Vaea while he is unable to train to help get him back to full health.

The Brumbies first discovered a clot in Vaea's calf in October and he was immediately sent for more tests when his foot turned white at training. At some point Vaea had a mini heart attack, which compromised the heart muscle. It affected his circulation and bits of the clot were pumped around his body.

Ironically, the pain in his calf saved his life, as doctors discovered a significant problem.

Vaea will have another test in six months to see if his condition has improved and a decision will be made then on whether he will be allowed to return to training.

The blood-thinning medication makes it too dangerous for Vaea to play or train due to the risk of internal bleeding, especially from a head or chest knock.

Had Vaea continued to play with the clot undetected, it could have caused a stroke or cardiac arrest.

''He's part of the Brumbies family, it's just the tradition of the Brumbies, and we want to give him everything we can,'' White told The Canberra Times. ''We want to help him, he's a young boy and with a great future and we want to make sure he still has that great future.

''Five minutes into a practice he couldn't walk and there was a clot running up and down in his system.

''I'm really proud of our medical staff, they've got in on this early and they've looked after him and that's a positive thing for the players here, they know they will be looked after.''

Vaea is having regular ultrasounds and check-ups and the lesion on his heart has decreased in size.

Vaea has played 26 games for the Brumbies after making his debut in 2011. His aggression and power game added punch to the Brumbies forward pack and he was likened to Wallabies great Toutai Kefu.

While he has been ruled out for this season, no decision has been made on his long-term future.

Brumbies doctor Angus Bathgate said Vaea's life would have been at risk had he kept playing. ''At the end of the day, the clot in his leg probably saved his life,'' he said.

''It could have easily gone to his brain and he would have had a stroke. It's scary stuff. You don't expect it in young football players. He's being well looked after now. It's unusual, it's not typical but it is being well managed and he's feeling normal.''

Vaea was originally part of White's 35-man squad. But he was not included when the Brumbies had to submit a final list to SANZAR before the start of the season. That means the Brumbies have one full-time roster spot open for this year.

The Brumbies begin their campaign when they take on the Queensland Reds at Canberra Stadium on Saturday night.

They are trying to make the finals for the first time since 2004 and no decision has been made on who will fill Vaea's roster spot. Captain Ben Mowen will pack down at the back of the scrum with Fotu Auelua adding punch from the bench.

White said Vaea would not be forgotten despite his illness keeping him on the sideline for the year. ''It's not like it's just a conveyer belt down here, we don't just spit out players when they can't play,'' he said.

''They come here, we look after them and all of their wellbeing. I want to turn the players into better people, and medically we're not going to milk them and milk them and then burn them out.

''I trust my medical staff, we've managed this and I'm proud of that because if we had a gung-ho approach and made him keep training, he could have had a stroke.''

Coaching staff and players have visited Vaea in hospital and he was at Brumbies training on Thursday.

BRUMBIES TEAM: 1. Ben Alexander, 2. Stephen Moore, 3. Dan Palmer, 4. Scott Fardy, 5. Sam Carter, 6. Peter Kimlin, 7. David Pocock, 8. Ben Mowen, 9. Nic White, 10. Matt Toomua, 11. Clyde Rathbone, 12. Christian Lealiifano, 13. Andrew Smith, 14. Henry Speight, 15. Jesse Mogg. Reserves: 16. Siliva Siliva, 17. Ruaidhri Murphy, 18. Colby Fainga'a, 19. Fotu Auelua, 20. Ian Prior, 21. Joe Tomane, 22. Robbie Coleman.