The 36-year-old spent two years away from Stamford Bridge with Chinese side Shanghai Shenua and Turkish giants Galatasaray before returning to Chelsea this summer.
"He can play a key role, but we have to build the profile of that key role," Mourinho is quoted as saying by London24.
"A key role can be to be there when the team needs a player to be there. For this Didier was always a fantastic example of a team player, of a club man, of a dressing room man.
"A key role is not for sure to play 50 matches in a season or to play every two, three days, 90 minutes of each game. At the age of 36, after so many years of experience he has even better conditions to be a key man."