Mata was inspirational in Chelsea's 4-1 win over Norwich City yesterday and he will not risk injury playing for his country over the next two weeks.
"I am surprised and I am very happy that he stays with me," Chelsea's official website quotes Di Matteo as saying.
"I feel for him because he's in great form. I don't know the reasons why but we as a club are happy he is going to be with us."
Chelsea are four points clear at the top of the Premier League after seven games.