Southgate named players who were returning from injury in his squads for both tournaments, with Harry Maguire and Jordan Henderson selected for Euro 2020 and then Kyle Walker last winter, despite the trio missing the opening games as they fully shook off lingering issues.
The England boss said about the return to 23-man squads: “It makes it a different sort of thought process, because you’ve had that leeway in the last couple of tournaments to take players that weren’t going to be fit for the first couple of games, or a bit of cover in a couple of positions that you might or might not have needed.
“This time, the physical condition of the players is going to be really important, the ability of players to bat out six or seven games.
"We know, having been to the latter end of two tournaments, the physical demands of that were far greater than we would have known, had we not been through that experience. We know that that’s a huge requirement.
“If you can only take two for each position, then players that are adaptable are helpful, players that can play more than one position are helpful.
"But equally, players that are physically vulnerable we’ve got to think very carefully about. I wouldn’t say all 23 [need to be totally fit], but we can take far fewer gambles than we were able to to the last two tournaments where it was 26.”
Addressing England’s lead-in to the tournament which begins on June 14, Southgate said: “We would be looking for a couple of friendlies, because by the time the Premier League season finishes, physically players would need a game.
“We’re still working out who that might be, because that will depend a little bit on who qualifies and who doesn’t, and who’s got other fixtures.
"So we are working those things through. We’ve got an outlined plan, but some of the detail relies on other things still falling into place and the draw for the Euros as well.”
“I didn’t enjoy the performance” he admitted. “I thought we were a little bit anxious at 1-0 and at 2-0. We started to chase the game a little bit where we didn’t need to.
"I think the fans will accept the players have been fantastic this qualifying campaign. They [the players] know they’ve got to hit higher levels in games to come.”