The England boss has revealed he can't guarantee the goalkeeper a place in his Euro 2024 squad should he continue to play second fiddle to David Raya.
Ramsdale has been included in the latest Three Lions squad for upcoming qualifiers against Malta and North Macedonia.
However, the 25-year-old has been ousted as Arsenal's first-choice goalkeeper since Raya's arrival from Brentford, making just two appearances since September.
"I think longer-term, we're just going to have to see how it is. I had that conversation with him in the last camp," Southgate told reporters.
"He's still battling to be the number one at Arsenal, and his profile and the way he can use the ball with his feet, we like, we think that's important.
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"But there is a reality as a keeper, if we get to March and he's six months without playing regularly, then I'm never going to promise things that I couldn't guarantee delivering."
Ramsdale has been linked with a move away from the Emirates Stadium, with London rivals Chelsea among the clubs reportedly interested.
But Arteta has ruled out a January move away for the ex-Sheffield United shot-stopper, who he says is firmly in his plans.
"First of all my door is open to speak about any player," the Gunners boss said.
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"We just want the best for our players and we try to do that, and we know the influence that we can have - sometimes positively, sometimes not so positively, towards them.
"We will always try to do our best to help them, but this is a team sport that needs 24 players that have to fulfil a role. And the role that you have in August, it might be very different to the one you have in March.
"So making early decisions, in my experience, is not something good at all and as well because the team has certain needs that has to be accomplished. And in order to do that you cannot do it with six, 10 or 14 players. It is impossible. So you need everyone and Aaron has a really important role in the team.
"I have no messages for any clubs [who may look to sign Ramsdale]. I can talk a little bit about my players, how much I like my players, how much I like Aaron and that we want Aaron with us, that's for sure."
Ramsdale is expected to be one of the substitutes as Arsenal take on Burnley in the Premier League on Saturday.
Arteta also revealed he could be without eight stars for the clash against the Clarets.
Skipper Martin Odegaard is a doubt, while Bukayo Saka and Takehiro Tomiyasu went off injured in Arsenal's 2-0 victory against Sevilla in the Champions League on Wednesday night.
Gabriel Jesus and Eddie Nketiah could miss out with hamstring and ankle injuries, respectively, while Thomas Partey, Emile Smith Rowe, and Jurrien Timber remain absent.
"Some of the injuries that we had, they are some bad luck, some of them have been long-term injuries with some special players and when we didn't have a lot of depth," he added.
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"We can talk about the depth, but after you have to talk about the specific positions or certain units where we are a little bit shorter.
"But it is the challenge of the season and other people have to step up, and that as well is a good test for the team - how we take those moments and how we actually respond to that. So far, the team is doing well."