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The 35-year-old has been unable to walk due to the mystery illness and admits it will be a long road to recovery.
Thompson was admitted to the Tsukuba Memorial hospital in Tokyo with a yet-to-be diagnosed illness, causing the player nicknamed "BFG" and "Wooly Mammoth" due to his size "excruciating pain".
The flanker, who represented the All Blacks in 29 tests between 2008 and 2012, was hospitalised after being rushed to A&E in the middle of the night.
"Christmas this year so far has been mostly spent in hospital with the BFG giving me the biggest fright in the 6 years we've been doing life together," she wrote on Friday.
"A few nights ago I had to rush him to A&E in the middle of the night & it's been one hell of an ordeal.
"But day three and things are finally looking up. There is still no official diagnosis (they suspect it's been a severe infection that's caused serious internal inflammation & excruciating pain)."
Thomson posted from his hospital bed on Tuesday that he had a long road to recovery ahead, while Gurunathan said they were hoping that he'd be able to walk again soon.
According to Gurunathan, the setback hasn't affected Thomson's famous sense of humour, with him giving fans the thumbs up and joking that he almost had his moustache amputated.
"But in all seriousness, it's been a tough week full of unexpected challenges. It's going to be a long road to get back on my feet but I'm up for it," Thomson said.
"I'm overwhelmed by all the love and support from friends and family all over the planet, words can't express what it means, I didn't expect such a big response. I'm humbled and my thanks and love go back to you all!."
Thomson represented New Zealand at secondary schools, under-19, under-21 and Sevens and played close to 100 Super Rugby matches for the Highlanders, Reds and Rebels.
He joined the Tokyo-based Canon Eagles in 2013.