Hall's arrival comes with Steven Taylor facing up to two months on the sidelines with medial ligament damage and Jose Enrique and Danny Simpson both also injured.
Hall will fill one of three key positions being targeted by manager Chris Hughton as the transfer window draws to a close.
He is also keen to land a left-back and a striker, and is hoping to push home his interest in Crystal Palace's highly-rated teenage forward Victor Moses.
The 19-year-old was withdrawn from the Palace squad which played at Newcastle on Wednesday evening by the club's administrators, and the Magpies are understood to have made their move with promotion rivals Nottingham Forest and West Brom also interested and a series of top-flight clubs monitoring the situation.
Hughton said: "It's been documented that we are very interested in signing the lad.
"Most people are also aware of the circumstances with Crystal Palace and the situation they are in, and we hope to make progress on that over the next couple of days.
"It's one we have a very, very keen interest in.
"He is a player who has an ability to score goals. There is a power and pace, but it is his potential.
"Around what we are trying to do here this season, which is the most important thing, there also has to be an eye on the future, and he is certainly a player of wonderful potential."
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