"It depends how good we want to be and what level we want to challenge at, but that's a clear indication of the task we've got".
"We're obviously coming off the back of a successful summer, so I think there's a good foundation for us to build on", Southgate added.
The other World Cup heroes who are now absent are Gary Cahill and Jamie Vardy, with the Chelsea defender and Leicester striker opting to step away from the worldwide scene and focus on their club careers.
Gareth Southgate has named his England squad, largely made up of the 2018 FIFA World Cup side, for their upcoming UEFA Nations League and friendly fixtures, and a few of the Three Lions' older regulars were not selected.
Midfielder Ruben Loftus-Cheek keeps his place after impressing in Russian Federation in the summer, despite playing just 22 minutes for Chelsea this season.More news: Apple's Next Smartphones and Watch Allegedly Revealed in New Leak
More news: England win toss and bat against India in fourth test
More news: Czech politicians pay tribute to late US Senator John McCain
He has also left the door open for Jack Grealish, Mason Mount and several other Championship players having picked Championship goalkeeper Jack Butland in his latest squad.
"Adam is one who would have been with us were he fully fit in the summer".
"Not many have to deal with the type of injury he had, and with a move at a young age to a club like Manchester United, and with England [playing in the 2014 World Cup] at 19".
"We had some mature conversations with Jamie Vardy, Gary Cahill and Ashley Young in terms of the desire to look at younger players". That is how I get the team going in the next couple of years, really.
It is considered too soon for the trio and Southgate insisted they will have to prove their worth to crack his squad. "Dalot and Romero will play in an U23s match, which is a first match for them after knee surgeries and they need that a little bit but it's good news for them because after that it's the worldwide break and then, after that, they'll be in a real condition to play".
"They all want to stay available and have all done a fantastic job with us".