But with the pair both away on international duty with Scotland, Weir has been chosen to start against Ireland.
The 22-year-old, who was out of action for six months after breaking his leg in Glasgow's RaboDirect PRO12 win over Ospreys last April, admitted his selection was somewhat unexpected.
But backing his close pal to bounce back from his omission, Weir knows they will continue to drive each other on.
"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 tomorrow," Weir told the Glasgow Evening Times.
"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."
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