'It's been a very long journey': The 39-year-old ex-Wallaby chasing a fourth Top League title

When he arrived in Japan 14 years ago in need of a break after a run of serious injuries, never in his wildest dreams did Daniel Heenan imagine he would be still playing rugby a decade-and-a-half later.

Turning 40 in November, the former Wallaby will line up for a sixth Top League final - and chasing a fourth title - when his undefeated Panasonic Wild Knights square off with Suntory Sungoliath on Sunday.

"It's been a very long journey, in a lot of ways," Heenan told AAP.

"Absolutely no way did I think I'd still be here. When I first arrived, I'd had a few major injuries and just needed a freshen up, and after the first few years I actually really enjoyed it.

"It just agreed with me and you buy into the program over here and create a few connections with the players, and here I am 14 years later."

Embracing the language and the lifestyle, Heenan and his wife Luisa have raised two daughters in Japan and the towering lock admits he is finding it hard to let go of the game.

His long-time coach, former Wallabies mentor Robbie Deans, is urging Heenan to go around again in 2022.

"It's a running joke with Robbie: 'another year, another year'," Heenan said.

"Robbie's been a part of Panasonic ever since I've been here. I trust Robbie as much off the field as I do on it and it's no surprise that he has success wherever he goes.

"He hates to lose at anything - even cards - but I love that about him. He's so competitive and it's infectious."

Heenan, though, accepts all good things must come to an end and is treating Sunday's final as his likely farewell appearance.

"At 39, I've got to look at life after footy but you never know," he said.

"My body's still hanging in there but there's a strong percentage that it could be (my last game). I've got to treat every game like it's my last."

He only played two tests, including his first under Eddie Jones way back in 2003, and 35 Super Rugby matches for the Queensland Reds and Brumbies.

But the former Australian schoolboys captain knows he cannot have his cake and eat it too.

"I can't have any regrets. I can't be unhappy with how my career's turned out," he said.

"I could have stayed and had another year in Australia and had another shoulder reconstruction, and my career would have been over."

As for life after rugby, Heenan, nicknamed Spud thanks to growing up on a farm in Gatton, has no firm ideas.

"I've got such a long list of careers that I've been copping a bit of grief from friends and family as to what I'm going to do after footy," he said.

"That's the running joke. Depending on who I'm speaking to, and who I get inspired by, it ranges from being a farmer to being a stockbroker to being a builder, an electrician. I really don't know.

"I've got a commerce degree, mum and dad are still out on the farm and my brother-in-law's a builder, so I'm sort of influenced from every angle at this stage.

"My brother's a lawyer. So there's opportunities. I've got to keep all doors open.

"I'm going to have to learn a whole new way of life and a whole new trade, which is exciting but it's daunting at the same time."