Lampard looks certain to play from the off in Tuesday's Champions League clash against Nordsjaelland in Denmark after failing to start the Blues' last three matches.
His omission for those games has fuelled speculation about whether the final year of the 34-year-old's current contract will herald the end of his glittering Stamford Bridge career.
But manager Di Matteo said: "Frank is still a key player and very important for us. He's been so successful with this club and I hope he stays for the rest of his career with us.
"Frank is an intelligent man and I have a very good relationship with him. We talk and, as much as nobody likes to be on the bench and being disappointed at not playing, I hope he understands.
"His attitude has shown he supports the team and that's very important."