But Blades boss Neil Warnock wants to do his utmost to keep him and is keen for Brown to sign a new contract before the end of the season.
"I am not surprised that Premiership clubs are interested in Michael because he has been outstanding for us all season," he said.
"But we have made progress in our discussions and the offer is now due to be put to the board for approval."
Brown has hinted that he may stay at Bramall Lane should they win promotion to the Premiership. They have slipped to third in Division One after losing their last two league games since defeat at Anfield three weeks ago.