Chelsea's Willian in action
United announced the appointment of Mourinho as their new manager on Friday, with the Portuguese boss replacing Louis van Gaal in the Old Trafford dugout.
Chelsea's Willian with former manager Jose Mourinho
Mourinho will have a huge task on his hands to make United into a title contender again, and he also has questions to answer about his ability as a manager having struggled at Chelsea this past season, which led to his sacking in December 2015.
However, reports from The Sun suggested that, in an attempt to boost his squad at Old Trafford, Mourinho wanted to go back to Chelsea and snap up playmaker Willian in a deal which would cost around £60m.
The Brazilian playmaker was snapped up by Mourinho back in 2013, luring him from Anzhi Makhachkala - and with 19 goals for the Blues in his three seasons at the club, Willian has been a valuable player both with his play in the final third and his hard work out wide.
It would therefore be no surprise to see Mourinho want a reunion with Willian, but it would be a shock to see Chelsea sell - and the Daily Mail report that the Blues' new manager Antonio Conte will block any move from Mourinho to complete the deal.
Conte knows that selling Willian to a major rival would be a bad start to life in West London, and whilst fellow Brazilian playmaker Oscar may be up for sale, Willian seemingly won't be allowed to join United this summer.
Would you like to see United test Chelsea's resolve for Willian?