England manager Southgate insists Kyle Walker's international career is not over despite omitting him for a third-successive squad.
Southgate unveiled his 26-man squad with Kieran Trippier and Trent Alexander-Arnold the preferred options at right-back.
As well as Walker, there was no place for Aston Villa's in-form captain Jack Grealish or Manchester United midfielder Jesse Lingard.
Asked whether Manchester City full-back Walker's England career was over after amassing 48 caps, Southgate replied: "Absolutely not.
"We've been very pleased with the form of Kieran and Trent. (Trent's) form for Liverpool has been really exceptional. It's an area of the pitch where we've got high competition for places."
England need only one point from their last two qualifiers to reach next summer's Euros, and will be looking to secure qualification in the men's 1,000th match against Montenegro at Wembley next Thursday.
"It's an opportunity for us to qualify for a European Championship which is a very important moment for us," Southgate added.
"And it's the 1,000th England game – a momentous occasion for everybody and a pretty special to be involved with. As a manager you get a real feel for the history and privilege of leading the team.
"The squad itself is a little bit larger than normal, we've got a few injury doubts, so we've named a slightly extended squad."
On Grealish's absence, Southgate added: "He's a very good player – I've watched him closely this season. The reality of that is he's up against (Raheem) Sterling, (Marcus) Rashford, (Callum) Hudson-Odoi and (Jadon) Sancho in those wide areas.
"The competition in that area is high level – they're all good players, Jack's a very good player – I worked with him at the Under-21s so I know all about him. He's very close, he just has to keep playing the way he is, and if we had issues over the weekend I wouldn't hesitate to call him into the squad."
Winger Hudson-Odoi was named in the Under-21 squad rather than the senior set-up last month after recovering from injury, and scored twice on his first start for the Young Lions.
"We were surprised at how quickly he was back," said Southgate.
"He's still on his way back, of course – he's a young player so he's still learning and improving but in the games he's played, you can see his level and he's pushing those players in the wide positions to start in the team.
"He acquitted himself brilliantly with the Under-21s so we got exactly the response we'd hoped for."
