De Rossi elbowed Brian McBride in the face during the 1-1 draw at Kaiserslautern last Saturday opening a wound under the U.S. forward's left eye that required three stitches.
Mastroeni was sent off at the end of the first half after a late two-footed tackle on Andrea Pirlo.
De Rossi was also fined $8000 while Mastroeni was fined $6000 FIFA communications director Markus Siegler said Friday.
De Rossi would be available to play in the World Cup final if Italy makes it that far. The United States was eliminated in the first round.
The Italian Soccer Federation said FIFA would have given De Rossi a five-match ban but reconsidered because of his written apology.
"I'm sorry for him that he's got to miss four matches but that's what we expected said Giancarlo Abete the head of Italy's World Cup delegation. Abete said Italy would not appeal the ban.
"We're going to accept FIFA's decision calmly said Abete. "We hope he plays again (at the World Cup) -- for his part and also selfishly for the rest of us."
FIFA president Sepp Blatter who issued a pretournament directive to referees to crack down on the kind of elbowing incident that De Rossi was suspended for would not comment on a decision made by the disciplinary committee.