The former Gunners star joined Barcelona in a £15m deal in the summer, but has yet to make his debut under Luis Enrique due to injuries.
Bringing in a new defender has become a pressing concern for United, who have been beset by injuries this term.
Louis van Gaal is thought to be lining up a £47m move for Borussia Dortmund defender Mats Hummels, but it remains to be seen whether he is an attainable target.
The Gunners in the meantime have also struggled defensively, even though Laurent Koscielny could feature against Dortmund in the Champions League tonight (7:45pm).
GETTY
Thomas Vermaelen has yet to make his competitive debut for Barcelona
However, the latest news concerning Vermaelen will surely come as a blow to Arsenal and Manchester United.
Spanish paper Sport claims Vermaelen's future is under threat after picking up a hamstring injury.
It is thought he could be out for up to five months and is expected to undergo surgery.
Vermaelen made 150 appearances for the Gunners during his five years in north London.
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