He is joined by a number of new faces after Johnson awarded debuts to 10 players during the quadrangular tournament hosted by the Springboks in June and which also featured Samoa and Italy.
But Weir - who started for the RBS 6 Nation clashes with Wales and France earlier this year as Scotland posted a third-place finish - was always confident his displays during the championship would mean Johnson would reserve him a place once he returned to fitness.
Weir hopes to be in the starting XV to face Japan on Saturday when it is announced later on Tuesday and told Press Association Sport: "Finishing the Six Nations with two starts was amazing and I enjoyed every minute of it.
"But seeing the boys out in South Africa when I was stranded on my sofa with my leg in a cast was not easy.
"However, those memories of pulling on a Scotland jersey were what pulled me through my rehab because I was desperate for more.
"I wasn't worried about losing my place though. After doing well in the Six Nations, I was confident that would be in Scott's head come my return.
"But now I need to confirm what he thinks about my by doing well in the Autumn Tests. I need to prove all over again that I'm good enough to play wear that Scotland jersey."