The Chile international struggled for both form and fitness following his transfer to Old Trafford from Arsenal in January 2018 when Mourinho was still in charge at the club.
Sanchez failed to make much of an impact at the club and after struggling for form last season, he was shipped out on loan to Inter Milan for the current campaign.
It remains to be seen whether the 30-year-old will be able to rediscover his top form in Italy this season.
And former Red Devils boss Mourinho has now opened up about Sanchez’s failed spell at Old Trafford so far.
Speaking in an interview with The Telegraph, Mourinho said: “Sanchez… I felt him [to be] not a happy man. And I think in every job you have when you are not happy it is not so easy to perform at every level.
“And maybe I am wrong. Maybe it was me who was not capable to get into him and to get the best out of him.
“As a manager sometimes you have the capacity to get the best out of the players and other times you are not successful in that approach.
“But the reality is that I always felt [of Sanchez], ‘a sad man’. So probably in Italy he will recover this. I hope he can. I always wish well to every player.”
Manchester United will return to Europa League action on Thursday night when they take on Astana at Old Trafford.
The Red Devils will then travel to West Ham United in the Premier League next Sunday afternoon.
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