The 23-year-old has been suffering from a hamstring injury in recent weeks and Di Matteo has hinted that he may not be fit until the September 15 clash with Queens Park Rangers.
Di Matteo said: "Marin is still out. Apart from that, we're okay.
"It won't be long for Marin but he might not be back before the international break."
Chelsea face Reading at Stamford Bridge on Wednesday evening.