Southgate admits injured Luke Shaw faces a fight to get into the final squad.
He says: "I have to say he’s up against it. He’s missed a lot of football.
"I’m not sure what is realistic at this time. I’ve liaised with Man Utd very closely. I’d have to say he’s a long shot."
Southgate insists young stars will get the chance to shine.
He says: "Everybody has a chance. The reason for a longer squad is we wer ein a similar situation before the last Euros.
"There are some injury issues that are very obvious and apparent and there are some that are more nuanced that we don’t have all the info on.
"Sometimes we need to see the players before making a decision. I think we can make better decisions with time."
Southgate says: "He’ll be a miss, there’s no doubt about that. He’s a fantastic human being. He’s been in that leadership role for a long time.
"We have young players with a lot of caps. There’s no reason young players can’t lead.
We’ve moved away a little bit from the defined leadership group. Sometimes when you limit that group it means others don’t step forward when they might and defy to a hierarchy.
"I want input from various areas. I have noticed occasions where, even with the captain and vice-captain, there’s a bit of deferential behaviour and we don’t want that."
On Henderson: "The 33 isn’t quite a fair definition because we’re taking a longer squad with some young players who we want to have a look at.
"The determining factor is the injury he had around the last camp. He missed five weeks.
"He’s a fantastic professional. It was a really difficult call to make. He’s been so supportive during my time here.
"Considering the disappointment, they dealt with it really well."
On Rashford, he says: "These are of course difficult calls. You’re talking about players who a important players and have
"I feel with Marcus there are other players who have had better seasons."
Gareth Southgate has previously backed Marcus Rashford when his club form has been sub-par, claiming he has continued to play well for his nation.
But he has paid the price for his struggles this term under Erik ten Hag, who has reduced him to the bench in recent weeks.
Henderson, 33, is surprisingly left out given he has been a regular during most of Southgate’s tenure.
But the decision of the 81-cap midfielder to quit Anfield for Saudi Arabia last summer, even if he did leave Al-Ettifaq for Ajax in January, looks to have cost him.
Wharton, 20, has been a revelation since signing for Palace from Blackburn for £22million in January and has been rewarded with an inclusion.
While Reds centre-back Quansah, 21, who spent part of last season at Bristol Rovers, has emerged as a regular under Jurgen Klopp this term and been included.
Team-mate Jones, 23, was England’s best player last summer as they won the Under-21 Euros in Georgia.
From Tom Barclay
Marcus Rashford is OUT of England’s Euros squad after failing to make Gareth Southgate’s 33-man provisional selection for the tournament.
Jordan Henderson is the other big shock omission while Chelsea full-backs Ben Chilwell and Reece James have missed out too.
But Henderson’s former Liverpool team-mates Curtis Jones and Jarell Quansah have been included, as well as Crystal Palace sensation Adam Wharton.
All three are uncapped, as are Everton centre-back Jarrad Branthwaite and Burnley goalkeeper James Trafford who have also made the cut.
There was no place for Jadon Sancho, despite gearing up for a Champions League final with loan club Borussia Dortmund.
While Nick Pope, Fikayo Tomori, Levi Colwill and Kalvin Phillips also were left out.
GOALKEEPERS: Dean Henderson, Jordan Pickford, Aaron Ramsdale, James Trafford.
DEFENDERS: Jarrad Branthwaite, Lewis Dunk, Joe Gomez, Marc Guehi, Ezri Konsa, Harry Maguire, Jarell Quansah, Luke Shaw, John Stones, Kieran Trippier, Kyle Walker.
MIDFIELDERS: Trent Alexander-Arnold, Conor Gallagher, Curtis Jones, Kobbie Mainoo, Declan Rice, Adam Wharton.
FORWARDS: Jude Bellingham, Jarrod Bowen, Eberechi Eze, Phil Foden, Jack Grealish, Anthony Gordon, Harry Kane, James Maddison, Cole Palmer, Bukayo Saka, Ivan Toney, Ollie Watkins.
The squad will be announced in just five minutes, at 2pm.
Stay tuned for updates.
The England boss has to submit his final 26-man squad to Uefa by June 7, just nine days before the Three Lions' opening Group C game against Serbia.
They also play Denmark and Slovenia.
Southgate's squad will be available for the two warm-up friendlies.
England take on Bosnia & Herzegovina at St James' Park on June 3.
They then host Iceland at Wembley four days later.
Rashford is not the only big name to be left out.
Jordan Henderson, Ben Chilwell and Reece James will also be forced to watch the tournament from home.
But there are a host of surprise inclusions.
Curtis Jones, James Trafford, Eberechi Eze, Adam Wharton, Marc Guehi, Jarell Quansah, Jarrad Branthwaite, Levi Colwill and Dean Henderson are all said to be part of the squad.
England will play two friendlies before Gareth Southgate finalises his 26-man squad for Euro 2024.
The Three Lions are then set to begin their campaign against Serbia on June 16.
Here are England's upcoming matches:
Marcus Rashford will be hurting, but he can have no complaints.
His omission from Gareth Southgate’s 30-man provisional Euros squad has been a long time coming with his Manchester United form plummeting week on week.
And this term has seen England boss Southgate – a loyal selector of the United forward during his darkest moments – make one of the toughest calls of his tenure to date.
Rashford, 26, has scored just eight goals in all competitions for Erik ten Hag’s side this campaign – his joint-second worst return in his entire career.
He had a decent impact at the Qatar World Cup last November, scoring twice, and netted most recently in a 3-1 home win over Italy in Euros qualifying last October.
But they were just fleeting moments in what has been dismal period for the Red Devil. Hopefully this is the catalyst that will prompt him to turn his career around.
Gareth Southgate has reportedly included Jack Grealish in his provisional squad for Euro 2024.
The Athletic report that the Manchester City winger will be named in Southgate's preliminary list of players.
Grealish missed out on the March friendlies but played in all five of England's matches at the 2022 World Cup.
Marcus Rashford is not in England's provisional squad for Euro 2024, reports The Athletic.
The Manchester United winger was included for the March friendlies and was a key man for the Three Lions at the 2022 World Cup.
However, he is expected to miss out on the preliminary squad after a dip in form this season.
Anthony Gordon will be named in England's provisional squad for Euro 2024, reports Ben Jacobs.
The Newcastle winger enjoyed an impressive first full season at St. James' Park.
Gordon made his Three Lions debut against Brazil in March and won his second cap three days later against Belgium.
Gareth Southgate is expected to name around 30 players in his provisional squad for Euro 2024 today.
The England boss will then have until June 7 to reduce his preliminary list down to a final 26-man selection.
Southgate's final squad is set to be announced by the Three Lions on June 8.
James Maddison has reportedly been included in England's provisional squad for Euro 2024.
Gareth Southgate will name his preliminary list at 2pm.
Tottenham midfielder Maddison is set to feature, according to the Daily Mail.
Reece James has been left out of England's provisional squad by Gareth Southgate, according to The Athletic.
The Chelsea captain endured an injury-hit season and has not started a Premier League match since November.
He returned for two substitute appearances during the run-in but was sent off against Brighton on May 15.
Ivan Toney has been named in England's provisional squad for Euro 2024, according to The Athletic.
The Brentford striker was also included for the March friendlies against Brazil and Belgium.
Toney scored his first international goal in the draw with Belgium.
Kobbie Mainoo is set to be named in Gareth Southgate's provisional squad this afternoon.
The Manchester United youngster will be in the preliminary England selection, according to talkSPORT.
Mainoo made his debut against Brazil in March before a man of the match display in the draw with Belgium.
Jarrod Bowen is also in Gareth Southgate's preliminary squad, reports Ben Jacobs.
The West Ham star missed his side's final game of the season through illness.
However, he has kept his place in the England squad for the pre-Euros training camp.
Bowen has won seven caps since making his Three Lions debut in June 2022.
Jarrad Branthwaite is set to be named in England's preliminary squad, according to the Daily Mail.
The Everton defender was a standout performer for the Toffees this season.
Gareth Southgate handed Branthwaite his first senior call-up in March but he did not feature against Brazil and Belgium.
