Stuff reporter Jackson Thomas talks to Chiefs halfback Brad Weber during the teams promo work with Sky.

Former All Black Adam Thomson has joined the Chiefs for pre-season training, two years after recovering from a serious spine injury that left him bedridden in a Tokyo hospital for two months.

The 37-year-old, a member of the All Blacks' Rugby World Cup-winning squad in 2011, is one of eight replacement players training with the Chiefs and the 29-test All Black started his stint with the Hamilton-based side on Monday.

The former Highlanders, Reds and Rebels loose forward featured for Otago in last season's Mitre 10 Cup after playing in Japan with the Canon Eagles (2013-17) and the Utah Warriors in the United States last year.

GETTY IMAGES Adam Thomson played for Otago in the Mitre 10 Cup last year.

A Chiefs spokesperson told Stuff he was only signed on as All Blacks cover until early February at this stage, but said it was "highly likely" he would play in Friday's pre-season match against the Blues in Waihi.

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The Chiefs' All Blacks returned to training this week but none of them will play in Waihi. The Blues are hosting the Chiefs in Super Rugby's opening match on January 31 and their All Blacks who played in last year's World Cup in Japan are likely to return for the Eden Park fixture.

A potential, shock return to Super Rugby would be an outside bet for Thomson unless Warren Gatland's side suffered injuries.

ADAM THOMSON/INSTAGRAM Adam Thomson in hospital in Tokyo in 2018.

The Chiefs have tremendous depth in his position, loose forward, with All Blacks Sam Cane and Luke Jacobson and the likes of Tyler Ardron, Lachlan Boshier, Mitch Brown, Pita Gus Sowakula, Mitch Karpik and Dylan Nel.

However, if the Chiefs were hit with an injury crisis akin to their last two seasons, Thomson could have another crack at Super Rugby for the first time since playing for the Melbourne Rebels in 2016.

He was with the Reds in Queensland in 2015, three years after his last appearance for the Highlanders, who he played for in 2006 and from 2008-12.

Thomson has already made a remarkable return to rugby after suffering from lumbar discitis, a painful infection of the spine, while in Japan two years ago.

The injury left him bedridden, unable to walk, and he was discharged in February 2018 after spending 57 days in hospital, forcing him to take an extended break from rugby.

Thomson made his comeback last year in Major League Rugby with the Utah Warriors before returning home and linking with the Takapuna club, then his old province Otago.

PHOTOSPORT Adam Thomson in action against the Chiefs for the Rebels in 2016.

"New year, new jersey," Thomson said via his personal Instagram account on Monday.

"Last week I was camping in the MacKenzie Country for some overdue kiwi-summer family time. Today I pulled on this jersey and mixed it up with 8 current @allblacks and a @superrugbynz side stacked with talent!

"It's a strange old beast this life we live, this time 2 years ago I was flat on my back in a Japanese hospital unable to walk. So never underestimate what the human body can do with a little self belief and a whole lot of hard work – persistence pays.

"Grateful for the incredible opportunity and warm welcome to this proud franchise @chiefsrugby. And as always, a massive thank you to my partner, family, friends, and rugby fans out there that keep helping to make this journey possible.⠀⠀⠀⠀⠀⠀⠀

"Day 1 done, but we're just getting started. Rent's due. Let's go to work!"

Also on standby with Thomson at the Chiefs are props Ross Geldenhuys (Bay of Plenty), Rob Cobb and Ollie Norris (both Waikato), hooker Donald Maka (Counties Manukau), lock Tupou Vaa'i (Taranaki), loose forward James Thompson (Waikato) and halfback Leroy Carter (Bay of Plenty).