The Portuguese has decided that the former Fulham centre-half is not good enough to command a starting berth and he is actively seeking a new partner for Eric Bailly.
With a move for Barcelonas Samuel Umtiti looking more and more unlikely as he closes in on a new deal at the Camp Nou, Mourinho has adjusted his list of targets.
Smalling may well find himself replaced at Old Trafford by international team-mate Harry Maguire, who would be available for £35million, according to the Mirror.
The Leicester defender has already dislodged Smalling in Gareth Southgates England team.
Mourinho remains a big fan of Real Madrids Raphael Varane and Paris Saint-Germain centre-back Marquinhos but accepts that a deal for Maguire may be easier to conclude.
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