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Laid up in hospital in Japan with a serious spinal infection around Christmas time in 2017, the chances of Thomson getting back on the field looked remote.
But that time in the sick bed sowed the seed for the former All Black to play the oval-ball game again.
''I got pretty knocked around. The recovery from that was a long frustrating process but I kind of made that decision early on that was not going to the last chapter of my rugby life,'' he said.
''I went through the ups and down, retrained how to walk again, went through the whole process, stripped it back to bare bones.
''It was pretty rough. Took a week to diagnose it. The pain you are in and you get specialist after specialist and scans coming back with no result. I made a decision that was not going to be the last time I played rugby.
''You want to close the book on your own terms. I'm a bit of a stubborn man. You don't want to be told by someone when to finish. I will tell myself when that time comes.''
He had no grand designs on playing at the top level. He just wanted to play a couple of club games and prove he could play again.
Through a lot of hard work, the loose forward got back to some level of fitness - it took 18 months. He signed to play in the United States but visa issues scuttled that.
Thomson (37) eventually played for Takapuna in the North Harbour competition last month.
''We had a really close win in the quarters and for me that probably ranks as one of my fondest memories of rugby - that is my end journey of recovery. Even though it was not the biggest occasion, it was great. I was out on the rugby field again.
''It was a massive accomplishment. There are times when you doubt yourself and the body doesn't work like it wants to. You get down and frustrated. You just keep going. I wasn't going to quit. Stepping on that field was a special time.
''I was warming up and I went to go on the field and in the back of my mind I was thinking 'what are you doing?' These 19 to 20-year-olds are going to run rings around you. Get out of it. But as I got on the field it was like riding a bike. A couple of tackles and it felt like home again.''
Otago assistant coach Tom Donnelly contacted him and the offer from Otago materialised.
''To be honest, it was a strange feeling driving back into the city limits. I had such a massive part of my life down here.
''I had so many fond memories and then to have a break and come here again - it was almost a bit emotional. Now coming into headquarters and having the golden O on. It feels good.''
He has signed on for six weeks for a start. He is available to play but it is also about helping out off the field.
''I made my Otago debut in 2004 so do the math on that one.
''I saw my name on the board there, still holding a speed record, the 10m sprint. But I will be nowhere near that.''