Cofie has joined the Blades on a season-long loan and becomes Danny Wilson’s first signing of the summer.
“John is another exciting prospect out of the Manchester United Academy,” Wilson told the club’s official website.
“He has the pace and the ability to cause defences all sorts of problems and most importantly he scores goals.
“We are delighted to have completed this deal as we think it will be very beneficial to all parties.”
Cofie spent last season on loan in Belgium with Royal Antwerp.