Louis Reed has joined Chesterfield on a season-long loan with immediate effect.
The 19-year-old will spend the 2017/18 campaign at the Proact Stadium, working under Gary Caldwell, as he looks for regular first-team football. Midfielder Reed has flown out to Portugal to link up with his new team-mates at their training camp.
United's youngest ever senior debutant made just one appearance for the Blades last season.
Boss Chris Wilder remarked: "I feel that Lou needs to go out and play first-team football to kickstart his career. Chesterfield, under Gary, is a good place for him to go and get games under his belt.
"We will monitor him, like we do all of our loaned players and hopefully he benefits from the switch."
Reed's departure is the fourth of the summer to date, with Ben Whiteman, George Long and Chris Hussey set for stints at Doncaster Rovers, AFC Wimbledon and Swindon Town respectively.