Squad sizes were increased from 23 to 26 at the previous edition of the Euros to mitigate the risks of teams facing a shortage of available players for certain matches due to possible COVID-19 cases and quarantine measures.
At the 2021 Euros, Harry Maguire and Jordan Henderson made the England squad while still recovering from injuries, while at last year's World Cup, Kyle Walker, James Maddison and Kalvin Phillips were included despite struggling with similar issues.
"We can take far fewer gambles than we were able to take for the last two tournaments where it was 26," Southgate told reporters ahead of England's Euro 2024 qualifier against North Macedonia.
"The size of the squad 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.
"This time the physical conditioning of players is going to be really important. The ability for players to bat out six, seven games...If you can only take two for each position, players that are adaptable are helpful."
England, who have already qualified for the Euro 2024 finals, top Group C with 19 points from seven games. They face North Macedonia in Skopje on Monday.
