England manager Gareth Southgate is considering returning to the three-man defence that helped his side reach the 2018 World Cup semi-finals.
Group A leaders England face Bulgaria in a Euro 2020 qualifier today, three days after being beaten 2-1 in the Czech Republic.
Defensive errors were punished in their first loss in a qualifier since 2009.
“We’re very aware and assessing those things,” said Southgate on a potential change in defensive tactics.
Harry Maguire, John Stones and Kyle Walker formed the back three at the tournament in Russia.
However, Stones is unavailable through injury, while Manchester City team-mate Walker has not been included in the squad.
“We are in a difficult situation in terms of the players that have played international football with us in that area of the pitch and who are playing regularly for their clubs,” added Southgate.
“That’s part of the reason we didn’t do that [a back three against the Czech Republic].”
Asked if there is enough time to make a change to his system before Euro 2020, Southgate said: “I think so. I think players take in tactical concepts very quickly, especially top players.
“We have to keep reflecting on what’s working and what’s possible, and learn from every experience we have.”