Steve Clarke says Scotland's young players need "time to grow and develop" after opting not to include Billy Gilmour and Mikey Johnston in his squad for the European Qualifiers against Russia and San Marino.
Gilmour has enjoyed a strong start to the season with club side Chelsea, making his Premier League debut against Sheffield United in August and earning praise from manager Frank Lampard after impressing in last week's 7-1 Carabao Cup win over Grimsby.
That sparked talk of a possible Scotland call-up for the 18-year-old - who has played nine times for Scot Gemmill's U21s - but Clarke is keen to give the country's youngsters more time to grow at youth level.
"Billy is an exceptional young talent and we have to give the young players time to grow and develop," Clarke said.
"I think the best place for them to do that is in Scot's U21s team. There are a lot of good boys down there."
Clarke also singled out Celtic winger Johnston, Hibernian defender Ryan Porteous and Fraser Hornby, who is on loan at Belgian club Kortrijk from Everton.
"I considered Mikey Johnston as well, who has been in terrific form for Celtic," the Scotland boss added.
"Ryan Porteous has got back in the Hibs team and looks a decent prospect and Fraser Hornby up front looks a handful.
"Scot's got some good players there and it's important that they grow together as a group. If they can develop and get a winning mentality then that'll be good for Scotland in the future."
Clarke gave call-ups to Dundee United striker Lawrence Shankland and uncapped Sheffield United midfielder John Fleck on Tuesday when he named his squad for the trip to Russia on October 10 and the home clash against San Marino three days later, both live on Sky Sports Football.
There was a recall for Oliver Burke, who came off the bench to score the late winner against Cyprus in June but was left out of Clarke's last squad.
Live Euro 2020 Qualifiers
Live Euro 2020 Qualifiers
Former Kilmarnock boss Clarke highlighted the importance of having an open mind but believes sticking with Scotland's existing players will pay dividends.
"I think you always have to be open-minded. You have to be prepared to try one or two different things, but it's also important as well that I keep faith with the players that I've got," he said.
"I believe they're better than they've shown recently and I believe over the coming games they'll show that to the public as well."
There was no place in Clarke's squad for midfielder Stuart Armstrong, who has only featured as a substitute for Southampton so far this season, while Matt Phillips is also absent as he will undergo a minor surgical procedure during the international break.
Left-back Kieran Tierney has not been picked after only making his debut for new club Arsenal last week following a lengthy spell on the sidelines.