The 36-year-old spent 22 years at the Blues, racking up 717 appearances for the club as he helped them to 15 major trophies.
However, Terry struggled to keep his place in the Chelsea team under Antonio Conte this season, making only nine appearances as the west London outfit marched to the Premier League title.
Di Matteo told beIN Sports: “He was a leader in the dressing room, he was the reference point for many players, especially many new players. He represented the true feelings of Chelsea.
“It's going to take a bit of time for somebody to step in and take that kind of role.
“I'm not sure if ever somebody will be able to do so, but certainly taking on the captaincy role and being that important for the team.”
Birmingham manager Harry Redknapp recently expressed his desire to sign Terry, while the likes of West Brom and Bournemouth have also been linked with moves for the veteran centre-back.