The Germany international was a part of his home nation’s stunning World Cup win in 2014 and has been a big hit since leaving Everton as a youngster in 2012.
Mustafi failed to make the grade at Goodison Park, but impressed with Sampdoria, tempting Valencia to move for his signature, and he’s since been a hit in La Liga.
And reports claim that Los Che are aware that they’re facing a battle to keep their man this summer, with Man United one of a host of teams interested in him.
It’s understood that Barcelona and Bayern Munich are also keen on the 23-year-old, but the Red Devils may be able to offer him guaranteed playing time.
Louis van Gaal’s own defensive ranks have been stretched to the point that he’s frequently used midfielders Daley Blind and Michael Carrick as makeweight centre-backs this term.