The FA has all but given up hope of including Jude Bellingham in the senior England squad for the upcoming World Cup Qualifiers, with Germany's Covid restrictions seemingly insurmountable.
Southgate was keen to get the 17-year-old involved for the whole training camp, in the hope of getting him more international experience with June's Euros in mind.
Bellingham was first called up in November, when he made his debut against Republic of Ireland.
But regional restrictions in Germany, which at present would make it compulsory for Bellingham to self-isolate for 14 days on return to the country, have scuppered his chances. Sky Sports News has confirmed there was a change in the Covid rules for North Rhine Westphalia, where Dortmund is based, which was introduced late on Tuesday.
Dortmund have said none of their players will be allowed to travel with their country if it means they cannot train and play for their club when they return.
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One option under consideration was for Bellingham to play solely in the away game in Albania, thereby avoiding a trip to the UK, but that option also now appears as though it has been ruled out.
Southgate sees Bellingham as a key prospect, and someone who can thrive as England's box-to-box midfielder for years to come. But if - as now looks inevitable - he misses all three of England's games this month, there will be just two more internationals in which he can gain experience, before the summer Euros.
Bellingham became England's third-youngest senior player behind only Wayne Rooney and Theo Walcott when he came off the bench during November's 3-0 win over the Republic of Ireland.
The teenager, 17 years and 137 days old at the time, has already been omitted from the latest U21 squad with the youngster producing some eye-catching performances for Dortmund since joining from Birmingham City last summer.
So far, he has made 21 Bundesliga appearances and provided three assists.
England kick-off their World Cup qualifying campaign at home to San Marino on Thursday March 25 before facing Albania away (Sunday, March 28) and then Poland at Wembley on Wednesday, March 31.
Southgate's impossible job?
Gerard Brand on the Pitch to Post Review show:
"If you look at those players who are now in contention for the Euros squad, the shift since the last set of internationals in November is quite amazing.
"You're now looking at Luke Shaw battling with Chilwell for the left-back spot, or potentially Saka being used in a five-man defence, Ezri Konsa may even battle with his own Villa team-mate Tyrone Mings at centre-back. Does Tammy Abraham get in the team? Who is the goalkeeper? How on earth do you incorporate Sterling, Sancho, Rashford, Kane, Grealish, Foden, Mount, Maddison, Saka into the side?
"Quite a lot has changed since November. We talk about 'welcome headaches' a lot in football, but Gareth Southgate strikes me as somebody who likes continuity in his selections. He puts a lot of faith in players who have played well for him but maybe aren't on form or getting minutes for their club.
"There is always a collective criticism to every England team selection, as if the 23 or subsequent XI pick themselves. It's actually an impossible job for Southgate.
"The England camp is an environment where you meet for no more than a week at a time, and in this case there's been a four-and-a-half month gap between meetings, so you have to have continuity in there in faces, personnel, and playing style. You can't just pick the most in form players in 2021.
"So there will be the inevitable 'Why hasn't he picked x and y?' questions, but Southgate is somebody who has his own vision for England."