The Colombian striker struggled at Manchester United last season, scoring just four goals in 26 games, but Mourinho thinks his new signing will be motivated to show what he can do.
He said: "He is not happy that in England people think he is not as good as he is and his motivation is there. He did a lot of things to come to us. He lost money to come to us, he didn't want to listen to other offers. He helped us a lot to do a deal with Monaco.
"So all these things together we think we can help him and he can help us."
The Chelsea boss has also seemingly ruled out a move for Paul Pogba after revealing he is not in the market for a midfielder despite the Frenchman's talents.
He said: "Pogba is one of the top players in the world. Pogba goes to any team and improves that team automatically.
"If he stays at Juventus, Juventus will be very strong again. If he goes somewhere else he will improve immediately a team.
"I think everybody has an interest in Pogba. But there are things you can do and things you cannot do.
"I love the Eiffel Tower but I can't have the Eiffel Tower in my garden. I can't even have the Eiffel Tower of Las Vegas."
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Paul Pogba looks likely to stay at Juventus
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Everton have placed a £30 price tag on John Stones but Chelsea are confident of getting their man.
Sunday Express Sport can reveal Mourinho has made 21-year-old Stones a priority signing this summer after viewing him as John Terry's eventual successor.