Reports from The Independent suggest United are prepared to pay £35m for the Croatian international. However, Inter are searching for a fee closer to £50m.
Perisic is highly rated at United, but they will refuse to pay, what they believe is, a bloated fee.
Instead, Mourinho will turn his attention towards Willian, who flourished under the Portuguese's tutelage when he was manager of Chelsea.
The Brazilian has recently committed his future to the Blues, although Mourinho will be hoping to tempt the 28-year old with increased playing time, after he found himself used sporadically under Antonio Conte this season.