Terry retired from international football this week in anticipation of his FA ban.
Di Matteo said: "He still has many years to play to come. I don't know what the future will hold.
"He likes to focus on the football, and that's all I have to be concerned about.
"I know that John loved playing for England. It was his childhood dream. It was a very difficult decision for him to take.
"When he wants to discuss the reasons, I'll leave that to him."
He added: "It certainly increases the chance to play a bit longer when you don't play internationally."