Garrett said Romo had surgery Friday to repair a herniated disk. No timetable for Romo's return was given but he is out of Sunday's final regular-season game and any playoff games Dallas advances to this season.
The Cowboys end their regular season Sunday versus the Philadelphia Eagles with the NFC East Division title at stake. Dallas has to win to make the playoffs; Philadelphia advances with either a win or a tie.
Kyle Orton, who has appeared in three NFL games over the past two seasons, will start at quarterback for Dallas against the Eagles. Jon Kitna, a 16-year NFL veteran who last played in the league two seasons ago, signed with Dallas this week to serve as a backup.
"The surgery was done as a result of the injury that happened in the game against Washington and Tony will be on IR," Garrett said. "Kyle Orton will be our starter in the ballgame. We spent the week exhausting all options in regards to Tony's situation -- treatment, rehab, all the different things, consulted a lot of different people on this. We just felt like as we discussed it, as (Thursday) wore on, that this was the best decision for him and for our organization moving forward."
Romo, 33, was injured in Sunday's game and doubts about his availability for the Philadelphia game were raised early this week. He received an epidural Monday but he missed practice Wednesday and Thursday.
Romo has been the Dallas starting quarterback -- when healthy -- since 2006. He completed 342-of-535 passes for 3,828 yards and 31 touchdowns this season. He was also intercepted 10 times.