"He has realised that he used language that was inappropriate and he has apologised for that and has certainly learned from that issue," said Di Matteo.
"And with good performances and good behaviour in the future he should still be looked upon as the leader for our club."
The 31-year-old centre-back is set to captain the side wearing an armband bearing the slogan 'Unite Against Racism' as part of a Football Against Racism in Europe (FARE) campaign scheduled for this week.
And Di Matteo added: "I've never been concerned about picking him.
"He's been able to focus on the games and that's what the players love to do, playing football and it's good for them that they can focus on that.
"What is common for players is that, even if they have family problems or some kind of issues outside in their private life, they tend to be able to focus on the football because it kind of just helps them."