A shattered Vaea told his Brumbies teammates and staff on Monday that he was announcing his immediate retirement from rugby after scans showed a recurrence of a blood clot condition that could have killed him.

The Brumbies were left devastated by the news almost four years after Vaea was first told he would never play rugby again.

Vaea had symptoms of the heart condition throughout pre-season training but medical staff were happy with how he managed the condition until his leg was starting to swell up, forcing him to leave the field in his last game against the Waikato Chiefs two weeks ago.

Almost four years ago Vaea was put on blood-thinning medication to save his life which forced him to miss the 2013 and 2014 Super Rugby seasons before making a shock comeback last year.

Brumbies players and coaches admired his fight after being told he could have died or had a stroke if he continued to play without medical assistance.

But after getting the all-clear to make a return last year, Vaea dropped more than 20 kilograms and rocketed into Wallabies selection contention with his impressive form and power for the Brumbies.

Vaea was set to play his 50th Super Rugby game this season.

Vaea was part of Wallabies coach Michael Cheika's Test camp last week, indicating that the 27-year-old was pushing for an international call-up.

Doctors recommended Vaea retire due to ongoing heart problems. Vaea could have had a stroke or died had the clots moved to his heart or brain.

​"I am extremely disappointed to be retiring today, under these circumstances," Vaea said in a Brumbies statement on Monday.

"It has truly been an honour to represent the Brumbies over the past five years.

"While my playing career has now ended, I consider myself extremely fortunate to have met and shared experiences with special players and coaches who I can call lifelong friends.

"It will be hard watching the boys run out, but I know that this is the best decision for myself and my family.

"Coming back from this last time was something I never thought I could achieve. I am so blessed that I was given a second opportunity. Now I have to concentrate on the next chapter in my life.

"While I am not sure what is in store for the future, I know that the lessons I have learnt in rugby will serve me well.

"It is an incredible game, has given me so much more than I could have ever dreamed and I will miss it immensely.

"Thank you to everyone who has made it such a special journey."

Vaea played 48 Super Rugby games for the Brumbies after his debut in 2011.

He was one of the most loved players and had a huge impact at the Brumbies despite his separate stints with the team.

When doctors first found clots on his heart, he was told he would never play again. He was put on medication and told to limit his physical activity to a "granny's pace" walk around the block.

"If I kept playing I could have passed away, I could have had a stroke and not been able to talk any more … I'm just happy," Vaea said in 2013.

"At first it was shock, it's still a mystery for me. But I'm just happy to be alive, I'm just looking at it in a positive way, things happen for a reason.

"I'm still young, I've got plenty of time to think about footy or if I'll be allowed to play again.

"Everything is heading in the right direction. If I come back I'll be very grateful, but if I can't I just have to accept it and move forward. There's nothing you can do, my heart is more important."

He ballooned out to 140 kilograms before being cleared for a comeback and vowing to make the most of his Super Rugby second chance.

"He is one of the most respected players from both his teammates and staff," Brumbies coach Stephen Larkham said.

"His determination to return to rugby after the initial diagnosis shows his true character.

"He took part in last week's Wallabies camp in Sydney, which shows you that he is currently regarded as one of the nation's top players.

"We will definitely miss Ita's contribution as a Brumbies player, but understand that there are much more important things in life than rugby.

"Ita has been a huge part of the Brumbies family over the past five years and it has been a pleasure to work with such an outstanding player.

"He has overcome the odds once before and we know he has made the right decision for himself and for the people closest to him."

It remains unclear whether the Brumbies will decide to sign a replacement or push ahead with one less player on their roster for the remainder of the season.

Vaea's announcement is a huge blow for the Brumbies as they prepare to play NSW Waratahs in Sydney on Saturday night.

Openside flanker David Pocock will miss the next two games through suspension, while Jarrad Butler trained on Monday for the first time after recovering from a knee injury.

Jordan Smiler trained in Vaea's No.8 spot on Monday and looks set to be given first shot at filling the position long term.

Before Vaea's announcement, Smiler said he would rise to the challenge should Vaea be ruled out.

"I'm always ready, you've got to be ready but we'll see what happens over the next few days," Smiler said.

SUPER RUGBY ROUND EIGHT

Saturday: NSW Waratahs v ACT Brumbies at Sydney Football Stadium, 7.45pm. Tickets available from Ticketek TV time: Live on Fox Sports 2