With the Three Lions dealing with issues such as injuries and European final absentees, the Football Association confirmed a larger provisional group would be announced on Tuesday rather than the definitive squad.
Southgate has named a 33-man party that will be trimmed down to 26 players on June 1, allowing him to include injury doubts such as Harry Maguire, Jordan Henderson and Kalvin Phillips.
Ben White, Ben Godfrey and Aaron Ramsdale received their first senior call-ups as Southgate selected Trent Alexander-Arnold among four right-backs in his larger pool of players.
As well as those players looking to prove their fitness, Southgate has 12 members of his squad still tied down to club commitments with the Europa League and Champions League finals.
“Really, I think our situation is more complicated than any other country at the moment,” Southgate said when asked why he had opted to name a larger initial squad.
“We have known for a little while that, of this 33, we’ve got 12 players still to play in the European finals this week so we were always going to need some additional players for the first part of our camp.
“Add to that, we’ve got some injuries that are at various stages – a couple that we have very little information about at the moment and a couple that are back into training or back into matches in Jordan and Jack Grealish but still not in training consistently, not training with the team in Jordan’s case.
“So we felt that more time is going to help us make better decisions. I’ve always said my preference was to name the squad as a clean 26. We were able to do that ahead of Russia (for 2018 World Cup).
“We had standby players that knew their role and that is always a preferable situation but we have not got an ideal hand of cards this time.
“There are a lot of unknowns. Information and evidence is really important when you are making decisions and we’ll have a lot more in the next seven days and we’ll be able to make the best possible decisions that we can.”
Southgate confirmed the Manchester United, Chelsea and Manchester City players in his squad are likely to get “five or six” days’ break before linking up with the group following their European finals.
“When we have talked with the players about the experience of the past, to have a break with their families is a preference to going away with the team,” he added.
“We think that is invaluable time as our aim is to be here for nine games including the friendlies and that is going to be a period of time where, from the start of the tournament onwards, there is a fair chance we won’t be able to see our families so we want to get that first part right and get everybody psychologically fresh.
“So it does affect who we can play in those first two friendlies. We have got to make sure that physically we give the players the right load. We can’t overplay the players we have got in those friendlies and we have also got players who might only be ready for 45 minutes in those games, or perhaps a little longer.”
One player who can link up is Liverpool full-back Alexander-Arnold, who was a surprise omission for March’s World Cup qualification triple-header.
He returns alongside Kyle Walker, Kieran Trippier and Reece James as one of four options at right-back.
“I could be drawn into talking about any individual and then get myself into a mess,” Southgate said when asked about Alexander-Arnold’s recall.
“I know people think I have an obsession with right-backs. I just see four good footballers. We go into a tournament with all sorts of flexible players that can fill different roles.”
Alexander-Arnold’s club-mate Henderson is also included despite not having played since February following groin surgery.
The 30-year-old is one of England’s most experienced players and part of the leadership group, with Southgate positive as to Henderson’s fitness.
“We actually think Jordan, the level of work he’s been able to achieve has been very high,” he said.
“What we haven’t been able to see yet is him on the pitch in a match situation.
“Although they are heading in the right direction, it is not an ideal situation. We’ve got four of those with Kalvin (Phillips) and potentially Harry Maguire as well. We are just monitoring those really closely.”
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