Mourinho made his comment ahead of Sunday's Premier League home game against Arsenal, the club where Spain midfielder Fabregas spent eight years before joining Barcelona.
"He loves Chelsea already," the manager told British newspapers on Saturday. "He's so happy, the way he plays, the way he's a member of the squad, the way he lives in this little blue village.
"It is like he's here for a long time. If you ask him now if he regrets the move, I'm sure he'd say no. If you ask him where he thinks he'll be in five years' time, he'd say he sees himself here in five years' time. He is Chelsea."
Mourinho acknowledged however that Fabregas, who joined from Barcelona in the close season, would always have a special place in his heart for Arsenal.
"He'll never lose that respect and connection with a club where he arrived as a kid and left as a top player," said the Portuguese.
"I wouldn't be happy if he came here saying 'I don't care about Arsenal, my life at Arsenal is over, I forget everything, now it's just about Chelsea'. I don't like that approach.
"After Chelsea I worked for Inter Milan and Real Madrid and I never stopped saying Chelsea were my club and that I wanted to come back one day. But I gave everything to Inter and Real," added Mourinho.
"Fabregas doesn't forget Arsenal ... the contribution it made in his fantastic career and that deserves a place in his memory and his heart. The fact he's giving everything to Chelsea with such professionalism and enthusiasm is exactly what we want of him."
Chelsea are top of the table with 16 points from six matches while Arsenal, looking to avenge last season's 6-0 drubbing at Stamford Bridge, are fourth on 10 points.