Sessegnon says Mourinho has instructed him to be more aggressive off the ball when playing at full-back and wing-back.
"I think he wants to vary me in different positions," he told Sky Sports News.
"If I am playing at full-back or wing-back he wants me to be aggressive off the ball - that's something I have been working on in my game.
"(He wants me to) be more positive on the ball as well. I've been a bit disappointed in myself, the way I have been playing recently. It's an honest assessment from me looking back at it.
"I'm usually a very positive player with the ball but the last few games I haven't exploited areas which I usually would. For the upcoming games, if I am involved, I will have to do better."