Weir has been chosen to start at the Aviva Stadium in Dublin as the Dark Blues take on Ireland looking to win their opening match for the first time since 2006.
His Glasgow colleague Jackson, however, has not even been selected in the match-day 23 despite kicking-off two of the country's three November Tests.
The 25-year-old was culpable for two of the four tries conceded in the 29-0 drubbing by South Africa at Murrayfield but Weir has backed his friend to put up a fight for the number 10 jersey ahead of England's visit to Edinburgh on February 8.
Weir, now fully recovered from the broken leg which saw him miss the summer tour to South Africa, told Press Association Sport: "It was a bit of a surprise to be picked ahead of Jacko. Even though I felt like I had put in some great performances for Glasgow lately and given the side a bit of spark, I didn't expect to get the nod to start the game on Sunday.
"Jacko is a good friend and we talk a lot about rugby, about our attacking shape and how we can punish teams.
"I know he will be disappointed but he's still been training well despite getting that bad news earlier this week, so I know he will be doing whatever he can to be back in the mix for the England match."
It was against Ireland last season that Weir cemented his reputation at international level after two brief substitute appearances.
The 22-year-old replaced the stuttering Jackson following a first-half in which the Irish had dominated with nearly 80 per cent of both the possession and territory without capitalising and helped see the Murrayfield hosts to an unlikely 12-8 win.
But the eight-cap stand-off admits he still struggles to see himself as Scotland's first-choice number 10.
"I remember my first touch against Ireland came from a counter attack when Johnnie Beattie chucked the ball to me," said Weir looking back 12 months. "I had to decide whether to kick it or run. I opted to drive forward and took us up about 30 meters up the pitch.
"From that we won a penalty which I put it deep into their 22 and we then got a bit of momentum. We clung onto the lead and in the last 10 minutes it was just a great atmosphere inside Murrayfield. It was hard to even talk to each other because it was so loud.
"It was a great start for me in last year's tournament. But even then I didn't really feel like a fully fledged international. Sometimes I have to pinch myself when I see myself wearing that Scotland jersey. I just try to live for the moment and enjoy it."
Jackson's cap hopes are not totally in the gutter after head coach Scott Johnson admitted earlier this month that he likes having the option of Weir's kicking prowess and the running power of his rival to choose from.
But Weir is working hard to make sure he is just as potent with the ball in hand as he is hitting it with his laces.
"When I first came onto the scene, everyone said I was a kicking 10," he said. "That is a good tag for me, because people don't expect me to be an attacking, running 10. That's what both Johnno and Gregor Townsend at Glasgow want me to become and hopefully I'm showing that now."
Ireland came within a minute-and-a-half of a famous victory over the All Blacks in their last match but Weir is not worried by what awaits his side in Dublin.
He said: "They nearly drove the world's best team off the pitch but it's a really good challenge for us to try to match a side capable of that.
"I believe we can go and attack them. We showed that our defence is solid last year after having just 20 per cent of the possession and still grinding out a win. The task is now for our attack to go there against a real physical defence that will look to hold us up with the choke tackle and succeed. I believe we are good enough to do the job."
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