Rovers were without a game at the weekend owing to MK Dons' involvement in the FA Cup and do not play again until Saturday - the first time they will have been in action since January 19.
Midfielder Martin Wood made his return from injury against a strong United team at the Premier League club's Carrington training ground. Doncaster lost 2-1, with winger Kyle Bennett scoring a good individual goal.
Assistant manager/player Rob Jones told the club's official website: "It was a good workout against a good United side and it has helped us with having no game last Saturday.
"It was good experience for the young lads Johnny Maxted and Liam Wakefield, who both had good games.
"Martin Woods got 50 minutes under his belt and came through alright, plus Kyle scored a good individual effort from the edge of the box."