Gareth Southgate is considering returning to the three-man backline that served England so well at the World Cup in a bid to shore up their leaky defence.
Dreadful individual mistakes in last month's 5-3 win against Kosovo were compounded by an even shakier defensive display on Friday, when the Czech Republic inflicted the Three Lions' first qualification defeat in a decade.
Harry Kane's early penalty was all too easily cancelled out by Jakub Brabec from a corner, with substitute Zdenek Ondrasek sealing a memorable 2-1 comeback win after England overplayed at the back and Jordan Pickford's clipped pass out was picked off.
Southgate felt a lot of the defensive issues in Prague came from "giving the ball too cheaply", as well as needlessly allowing the Czechs to show their set-piece prowess.
And while the 57-cap former centre-back did not feel the defence was England's biggest problem on the night, he is toying with the idea of returning to a back three flanked by flying full-backs.
"I think 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 with their clubs," Southgate said.
"So, that's part of the reason we didn't do that (against the Czech Republic).
"It's certainly something we've considered and I don't think we can dismiss.
"I'm not sure, ahead of Monday, if that's the right thing to do but we're very aware and assessing those things."
Joe Gomez, a favourite of Southgate, is in the squad but is not starting regularly for Liverpool, while uncapped Fikayo Tomori and Tyrone Mings join wobbly Michael Keane and established Harry Maguire as the centre-back options this time.
Asked if there is enough time to implement a defensive switch in system before Euro 2020, Southgate said: "I think so, I think players take in tactical concepts very quickly, especially top players.
"So, we have to keep reflecting on what's working, what's possible and learn from every experience we have.
"We'll learn a lot from (the Czech game). We've had straightforward qualifying games that haven't challenged us.
"(This) was a proper test and we didn't come through, so it would be naive not to take the lessons from what we've seen on the pitch."
Southgate is "under no illusions as to where we stand" and wants a positive response from his players in Monday's trip to Bulgaria.
England will qualify for Euro 2020 with a win in Sofia should Kosovo fail to beat Montenegro, but the loss in the Czech Republic will hurt – and perhaps provides a timely reality check as excitement builds ahead of playing much of Euro 2020 on home soil.
"Look, it's not for me to tell the public not to dream and not to have hope," Southgate said.
"I think internally, we have to be different and be realistic and we haven't changed our tone on that at all.
"We know our strengths and we know the areas we have to improve upon. We've talked about it throughout the week and we've had evidence of it (against the Czech Republic)
"So, I don't think any of us within the camp are under any illusions.
"To be a really top team, with players with experience of winning the biggest matches, we're still some way from that.
"But we found a way to progress through the World Cup with what was a relatively inexperienced team and that's what we're always trying to do: to find solutions to bring some good players through.
"The reality of football is you're not going to cruise through a qualifying campaign like we have unless you're a super experienced team who have a constant high level of performance.
"So, (this) isn't a night you want to be involved with because of the record there's been, and you never want to lose matches as an England manager, but it's something that will galvanise us and make sure that we look for a response on Monday and moving forwards."