Speight flew out of Sydney on Tuesday with titanium mesh on his skull and a surgically-repaired knee after a year of injury nightmares threatened to ruin his hopes of making it to Rio.

The ACT Brumbies flyer has defied the medical odds to make a comeback seven weeks ahead of schedule to join the team in what will go down as an Olympic miracle if Speight gets on the field.

But the last hurdle in front of him is a mental challenge as he prepares for the unexpected of being a travelling reserve who can only be called on if there's an injury.

The travelling reserve gets the Olympic experience with a twist, staying in separate accommodation and getting slightly different Australian gear if they're not used in the team.

But nothing can dampen Speight's spirits as he aims for a medal, declaring "I've got nothing to lose" as he puts his injury-riddled build-up behind him.

"I definitely didn't think I'd be back ... I thought when I injured my knee that my Olympic dream was gone," Speight said.

"Anything can happen now, I've just got to be ready. It's been the first time I've been out for so long with injuries and it's been tough.

"I don't get all the same kit and those things, but we're training with the boys every day and we'll still have access to the village every day.

"We're a pretty tight group and no one feels left out and no one will be left out. I've got nothing to lose after the year I've had so I'll just give it everything I've got."

Speight has almost spent more time in hospitals this year than on the rugby field after putting his Super Rugby title ambitions with the Brumbies on hold to chase Olympic selection.

His hopes were dealt a cruel blow when a head clash with Brumbies teammate Christian Lealiifano cracked his skull and required titanium mash to repair the bone.

That kept him out of action for three months and when he finally returned to play for the sevens, he injured his knee in an inter-squad trial match that doubled as selection auditions.

Speight was told he would need 12 weeks to recover. But he walked on to the plane bound for Rio just five weeks after surgery and ready to play again.

The injuries have limited Speight to just a handful of sevens games to prove his worth and four Super Rugby matches for the Brumbies this year.

"[Coach] Andy Friend has shown faith in me, the players and coaches have shown confidence in me so I'm going to give it a red-hot crack and give it my all," Speight said.

"The surgeon and the rehab staff have been amazing. I started running after two weeks, the healing and rehab has gone a lot better than anyone could have thought.

"I go in with the mentality that I had nothing to lose through this whole progress. If I made it, then I made it. If I didn't, I could walk away knowing I gave it everything.

"So it's a credit to all of the staff that I'm back up and going now and there's a good feeling around this group."

The sevens teams will base themselves in Porto Belo for the lead up to the Games before shifting into the much-maligned athletes' village.

Canberra schoolboy mates Tom Cusack and Lewis Holland are part of the men's Olympic squad while former Royals star Sharni Williams will lead the women's team on its gold medal charge.