Jose Mourinho desperately wants to bolster the position in the summer transfer window. The Portuguese has used Ashley Young as a stopgap solution this season, with Luke Shaw not earning the trust of his manager.
Danny Rose and Jose Gaya have been reported to be on Mourinho's wishlist.
But the Manchester Evening News claim Sandro is the 55-year-old's top priority.
That fee is believed to have risen to £70m now, and could continue to grow if Sando stars for the Selecao in June's World Cup.