United have agreed an undisclosed fee with Everton for the services of Dominic Calvert-Lewin.
The Toffees have substantially increased their initial offer for the youngster, which was rejected during the summer.
The striker, who has made just one appearance under new boss Chris Wilder, has now signed at Goodison Park, with the Blades set to benefit further from the transfer depending on the teenager's progress on Merseyside.
In total, the 19-year-old has made 12 appearances for the Blades, having made his debut at Leyton Orient towards the end of the 2014-15 season.
Speaking of the transfer of Calvert-Lewin, boss Wilder remarked: "This is a really good deal for us and a fantastic opportunity for Dominic. We do not want to stand in the way of a young player joining a well-established Premier League club."