He told the Telegraph: "The only thing I say is that it happens with almost everybody in some moments of your career: you lose a little bit the sense of who you are and what you have to be.
"The season after France won the (2018) World Cup, I think Paul came back different.
"The World Cup brought him into a dimension where football was not the most important thing for him. Sharing the philosophy of everyone; everyone with the same level of responsibilities."
Mourinho also says he felt he wasn't supported by the club's top brass when he chose to drop the midfielder.
"When you are supported by the power, by the hierarchy, the message that passes through is very positive in the group," Mourinho continued.
"When you are not supported because the player is more important or what the player represents is more important then you are in a fragile situation. Even if you are a coach with so much experience as was my case."
On Pogba's four-year ban, he concluded: "I am not enjoying Paul's situation at all."