The ready availability of Kitna, who retired from football after the 2011 season, surprised coach Jason Garrett, the San Antonio Express News reported Wednesday.
"Are you serious?" Garrett said he responded after Kitna sent him an email saying, "Hey, if you feel like I can help, I'd love to come help you."
"It just made sense to us," Garrett said. "He started a lot of games for us, knows this offense, knows this environment, and we felt like on short notice, he'd give us the best chance if he did in fact have to play."
Kitna played in the NFL for 15 years, his last three for the Cowboys. He now teaches math and coaches football at a high school in Tacoma, Wash.
"My career is done. I was happy with it," Kitna said. "I just knew the situation that they were in. I felt like I might be able to help."
The Cowboys signed Kitna Wednesday to back up Kyle Orton. He was at practice in the afternoon.