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As it stands, United's only right-back is Rafael da Silva, who has recently been sent home from the pre-season tour injured.
Micah Richards' development at Manchester City has been stunted by the emergence of Pablo Zabaleta. With just one year left on his contract, City are likely to be keen to sell Richards this summer to avoid losing him on a free next year.
Richards, who was a regular for England before Fabio Capello got the manager's job, is still only 26 years old and should have some of the best years of his career ahead of him.
City bought Richards from Oldham when he was a teenager and reportedly are owed a percentage of whatever transfer fee the club get for him according to the Manchester Evening News, meaning City will be keen to hold out for a higher price. However, with just one year remaining on his current deal and his status at the club clearly as a player who isn't needed, United should be able to sign Richards on the cheap.