Since Weir's total match time since he suffered a broken leg against Ospreys in the penultimate game of the 2012/13 RaboDirect PRO12 season has been accumulated in just a couple of outings for Stirling County, it is a bold move in such a hostile environment, the scene of one of the Warriors' worst defeats in the last campaign.
However, Townsend has faith in the young playmaker's ability to cope. "It is great to have him back," the coach said. "He missed two games at the end of last season and four this season, so to have a six-month injury and miss only six games is great. He has worked really hard on his rehab, he has played his two games now for Stirling. You can tell he is back up to the right fitness levels, confident with his movement and kicking and playing well too.
"Duncan is 22 but he is three or four seasons into his professional career now. He started two Six Nations games last year, so he is an experienced stand-off. This is an opportunity to see where he is early in the season."
Weir takes the place of Ruaridh Jackson, with cover from the bench provided by Scott Wight. Glasgow have already used 34 players over the course of their four PRO12 games this term, a number that would be remarkable for a struggling side but which is truly staggering for a team with a 100% winning record. "Every week you pick a team to win the game," Townsend said. "We have to manage the squad through the season and players are coming back from injury throughout the year. This is another good, strong squad."
In total, Townsend has made 10 changes to the side which won, albeit in a rather workmanlike manner, 24-17 against Zebre in Parma last weekend.
In the pack, an all-changed front row comprises Ryan Grant, Pat MacArthur and Moray Low, taking over from Gordon Reid, Dougie Hall and Jon Welsh respectively. Rob Harley drops back from the second row to the blindside flank, making room for Tim Swinson at lock, while Richie Vernon comes in at No.8 to replace head-knock victim Josh Strauss. Townsend has also made three changes to the three-quarter line, the most noteworthy of which involves Niko Matawalu starting on the right wing rather than at scrum-half where he made such a spectacular impression last season.
The Fijian has played Test rugby on the wing and at full-back, while he often moved to the touchline berth during the course of matches last season, and the Warriors' strength at scrum-half means that an impressive full shift on the wing could solve a running dilemma for Townsend.
Townsend said: "Niko is explosive, one of our quickest players. He is very, very creative, so when you see him at nine, he spends a lot of time putting other players into space. The same thing can happen on kick return so he is finding holes for other people.
"He just wants to get on the ball. He will be working hard to get on the ball so we have got to find ways to get it to him if it does not come from kick returns."
Glasgow's 29-6 loss at Parc y Scarlets last season is a bitter memory for Townsend and his squad, a performance and a result that did more than anything to rob them of their chance of the home semi-final they craved. Nor has it been forgotten, according to Swinson at least.
"I was on the bench and came on for the last 20 minutes," said the lock, who made his Scotland debut on the summer tour to South Africa. "It's something we've talked about this week and we don't want it to happen again. It's something we're really aiming to put right. We felt it was something that let us down last year."
Today's game will also serve as a reunion for many in the Glasgow camp as they come up against John Barclay, the flanker who brought his long association with the Warriors to a close when he moved to the Scarlets at the end of last season.
"The forwards will be looking forward to it," Townsend said of that aspect of the contest. "For me, I know what a good player John is and that he is playing well at the moment.
"He came back from a shoulder operation recently and looked in really good condition against the Dragons. Last week he got a couple of turnovers and a yellow card, which shows he was a thorn in the side of Edinburgh. He is a quality, quality player who played really well for us and who I know will want to play his best game against his former team."