Sanchez moved on-loan to Inter Milan in the summer.
He told the Telegraph: "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."