The Italian coach believes that the 31-year-old has cemented himself as a Stamford Bridge legend and is hopeful that an extension for the England international will be agreed.
The left back has been at Chelsea since his acrimonious move from London rivals Arsenal in 2006, but is out of contract at the end of season and would be able to agree a deal with a foreign club without the need for Chelsea's approval from January onward.
Talks have been ongoing over an extension and, speaking after Saturday’s 1-0 win over Stoke City, Di Matteo is confident that an agreement will be reached very soon.
"I'm very optimistic that it will be dealt with before that [January]," Di Matteo told reporters. "He has become a legend - he is now Chelsea through and through. But I wouldn't say it's just happened recently. He's been here many years and has contributed a lot to this club."
Di Matteo went on to praise Cole's attitude and professionalism, which has come in for criticism at times from his detractors, as well as the consistent quality of his performances.
"He's a fantastic pro, which I'm not sure whether you know," Di Matteo continued. "Somebody that's the first one out in training, one of the first into the building with JT [John Terry], trains every day like a professional, reliable, somebody that you could go to war with. And he's a very quiet guy as well. He's very private about his own stuff. He's one of the best left backs in the world."
Chelsea faces Championship side Wolves in the League Cup on Tuesday night, before traveling to the Emirates on Saturday for a crunch Premier League clash against Arsenal.