The pair are in fine form for the Owls this season and have driven the side to an unbeaten league start under Garry Monk since the last international break.
On-loan defender David Bates also misses out, as does Jordan Rhodes. Included is Wednesday full-back Liam Palmer.
In what has been an underwhelming Euro 2020 qualification campaign so far, Scotland play Russia on October 10, followed by a home match with minnows San Marino three days later.
Bannan told The Star last month that he was frustrated by a lack of interest from manager Steve Clarke, although he admitted the birth of his young daughter meant he was less keen on travelling for international duty to sit on the bench.
He hasn’t been included in a Scotland squad for over two years.
Bannan, 29, said: “I’ve spoken to Steve Clarke a couple of times and made myself available, but the squad has been announced and I’m not in it. It’s just one of those things.
“I’ve got to keep working hard for my club and what will happen will happen.”
Fletcher, who has 10 goals in 33 games for Scotland, has previously admitted that he is considering his international future. He last featured in their successful UEFA Nations League campaign last year, leading the line in wins over Albania and Israel.
He has scored five goals in the Championship this season, including four in his last five matches.
Called up for the first time, ahead of Fletcher, is 24-year-old striker Lawrence Shankland, who plays in Scotland’s second tier for Dundee United.