Maguire has been one of the first names on the team sheet during Southgate's time in charge of the national team, playing an important role in England's runs deep into the last two World Cups and recent European Championship.
His club form however has provided a stark contrast, dropped from the United regular starting XI this season with Raphael Varane and Lisandro Martinez now Erik ten Hag's preferred pairing at the back.
The former Leicester City is effectively United's fifth choice centre-half with Victor Lindelof and left-back Luke Shaw often preferred by the Dutchman.
The 30-year-old has started just seven league games this season but has kept his place in the England XI, named in Southgate's squad for upcoming Euro qualifiers against Malta and North Macedonia.
Speaking at a press conference on Wednesday, however, Southgate admitted the situation cannot continue in the long-term, suggesting players such as Maguire and Manchester City's Kalvin Phillips may need to find a different solution.
'Inevitably it's not a situation that can continue forever,' Gareth Southgate said of Maguire.
Southgate has also suggested his regular no1 Jordan Pickford could also find himself in a difficult situation should he be relegated to the Championship with Everton.
The Toffees head into the final day of the season two points clear of the bottom three in a three-way scrap for survival with Leicester City and Leeds United with Southampton already down.
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Everton take on Bournemouth on Sunday with their survival hopes in their own hands.
'That would depend on how well he was playing,' Southgate said.
'It wouldn't be ideal because clearly the level of attacks, finishing, speed of the game would be completely different so I think it would be difficult but let's see what Sunday brings.'
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