LOS ANGELES: The Dallas Cowboys officially announced the signing of veteran National Football League quarterback Mark Sanchez in one of several roster moves on Sunday (Monday in Manila). Sanchez was signed and young quarterback Jameill Showers was waived. Sanchez is expected to be the Dallas backup after being released by the Denver Broncos on Saturday. Rookie Dak Prescott will be the starter when the Cowboys face the New York Giants in their NFL season opener on September 11. The Cowboys also kept starting quarterback Tony Romo on the roster. Sunday was the first day Dallas could have placed Romo on injured reserve, which means he would be able to return later in the regular season. Romo suffered a compression fracture in his back in a preseason game against Seattle on August 25. It is estimated that he will be out six-to-10 weeks.