Richard Tanner, who writes for The Express, told talkSPORT that while the German centre-back is United's main priority, the North-West outfit may struggle to sign him because the 25-year-old is not keen on moving to Old Trafford.
Manchester United make Mats Hummels number one target?
Manchester United reportedly make Borussia Dortmund centre-back Mats Hummels their top defensive summer target.
Should Manchester United pursue Borussia Dortmund's Mats Hummels?
Smalling determined to be first choice>
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