The European champions allayed fears their captain had suffered a serious knee injury in Sunday's Barclays Premier League draw with Liverpool when they confirmed on Monday he would be out for weeks rather than months.
And with Chelsea having further assessed Terry over the past four days, Di Matteo had even better news to report on Friday afternoon.
"With JT, we're looking at approximately three weeks," he said.
"Fortunately, it's not as bad as we first thought."
Di Matteo added: "On the one hand, we're obviously pleased it's not as bad as first feared.
"On the other hand, we're disappointed we're losing him again after he just got back.
"It's a crucial period of the season for us, too. So that's a shame.
"It will depend on the progress of his rehab. We'll do everything to speed it up, but it depends how he reacts as well."