The New Zealand-born Scarlets No 8 was handed his first call-up by Gregor Townsend ahead of last autumn’s Murrayfield Tests.
But he was made to wait for his international bow as a nasty head knock sustained in the capital on club duty a week later ruled him out for all but the final two games of the season.
During five months out of action battling concussion-related symptoms, Thomson convinced himself he would be watching the World Cup from his sofa.
Thankfully, his worries were without foundation. The 28-year-old, who qualifies through his Wishaw-born grandfather, was finally able to pull on a Dark Blue shirt against France at Murrayfield last month, his 42-minute outing enough to convince Townsend he should be on the plane to the Far East.
“If you asked me a year ago if I’d be playing in the Rugby World Cup it would be a definite no,” admitted the back-rower. “It’s been a long journey and my family are super proud of where I am at the moment.
“Did I fear the chance had gone after the concussion? Oh yeah 100 per cent.
“I was selected in the autumn but had one game to play for my club against Edinburgh up at Murrayfield. I carried the ball, got knocked out and since then it was five months trying to work my way back to a point where the head bang was fine, I was injury free and able to play at a level where I was expected to if I was going to pull on the Thistle.
“It was tough – but you’ve just got to take it a day at a time. When they selected me in the training squad I was over the moon.”
There was one last panic before Townsend confirmed his place in the 31-man travelling party as Thomson was taken off in the France Test having sustained yet another bang to the head.
“That was more precautionary than anything,” he said with a look of relief. “They saw something that looked a bit, I don’t know, different. So they took me off. I had a minor headache but felt fine. But 100 per cent, I feared the worst. I thought: ‘Aw, there go my chances…’
“But they must have seen something because I’m here now.”