Former England international Martin Keown has told Gareth Southgate to revert to a three-man defence at the European Championship if Harry Maguire loses his fitness race.
Southgate included Maguire in his 26-man squad for the finals despite the Manchester United defender's struggles with an ankle injury suffered towards the end of the season.
Maguire is unlikely to feature in the opening group game against Croatia at Wembley on June 13 and Southgate has cast doubt on when the 28-year-old may be back in contention.
With Maguire out, John Stones is the only recognised central defender with more than 10 senior England caps – with Conor Coady of Wolves and Aston Villa's Tyrone Mings relative newcomers to international football.
With that in mind, Keown believes the best course of action would be for Southgate to once again move to a back-three and operate the same system which saw England reach the semi-finals of the 2018 World Cup.
"Maguire is playing in an area on the pitch where we are developing players but we are short of players," he said.
"Both starters at centre-half, I only counted 12 caps between them before the Austria game so that was quite an inexperienced central defence.
"If Maguire doesn't make it then with the players Gareth has picked he should shift back to a back-three and he could do that to great success.
"So it's a big miss if he is not there and it is about changing the system to a back-three because he is that important."
Keown, speaking as an ambassador for McDonald's Fun Football programme, revealed he has always been a fan of Maguire and believes the make-up of Southgate's squad means a back-three could be the way to go.
"I think we just find ourselves where we are developing new central defenders: Ben White and Ben Godfrey, Ezri Konsa at Aston Villa was no doubt close to a call-up," he told the PA news agency.
"There has always been a production line of central defenders, we didn't pick Eric Dier – I was a bit surprised he didn't pick Dier even though he is fairly new to that position.
"Maguire is key – he came in at 16 to make his debut for Sheffield United and I always felt that he had all the star qualities you need.
"His presence in both penalty boxes, the way he passes the ball, his calmness, decision making, and I think he is quick enough for international football with the right people around him.
"That is probably why Southgate picked so many right-backs in the squad because either Kyle Walker or Reece James can play in a three.
"There is flexibility, Coady could play in the middle with Stones on the outside, Gareth has given himself options, it is just not ideal that there isn't the number in terms of experience."
Martin Keown is calling on families to sign up for McDonald's free Fun Football sessions, which will get thousands of children playing football this summer. To find a local session go to: mcdonalds.co.uk/football
