The 28-year-old England man will be a free agent in the summer when his Old Trafford deal expires and he recently turned down what Sir Alex Ferguson said was the club's final contract offer.
Now, according to the Manchester Evening News, struggling Newcastle have made a firm offer for him.
Boss Sam Allardyce is under increasing pressure on Tyneside following that 2-0 midweek home defeat by Manchester City.
And he reportedly sees the addition of Brown as key to bolstering his side's shaky defence.
Allardyce is a long-term admirer of Brown, who has spent most of the season deputising for the injured Gary Neville at right-back at Old Trafford.
Ferguson must now decide whether to let Brown go now for a fee or lose him for nothing in the summer.
If he takes the first option it could leave him light at the back with Neville still having to prove his match fitness.
The options behind the skipper are John O'Shea and Danny Simpson.