Tottenham are assessing Sassuolo's Gian Marco Ferrari as part of their Europe-wide search to find a defender.
However, Mourinho wants to improve on his options with one starting quality defender.
According to 90Min, Mourinho is hopeful of upgrading the position, ideally with someone left footed.
Spurs have a budget of roughly £15 million to spend on a defender in January, hence them looking at 28-year-old Ferrari.
He is a key player for Sassuolo, but would be available for a modest fee.