The Nigeria international has come under scrutiny at times this season but the Italian boss is insistent in his belief that he performs a vital role for the team.
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"Over the years he has been almost ever-present," Di Matteo told Chelsea's official website. "He was very important at the back end of last season and this campaign he has started in good form.
"We all make mistakes in games and I don't think he gets the credit for the work he does for the team."
Having performed many of the same jobs in central midfield himself during his playing days, Di Matteo is mystified as to why the value of Mikel is not more apparent and appreciated.
"I don't know why Mikel is underrated by the media or the fans," he added. "He is very rated by us in the group and it's a position where you're a bit of an unsung hero.
"You do the dirty work which is not recognised all the time because the goalscorers and more creative players get the recognition. But he is very important for our team."