Dallas has to decide whether to place Romo on the injured reserve-return list after he broke a bone in his back in a preseason game at Seattle. Romo would miss the first seven games if he's on that list, and Sanchez could take that roster spot.
Defensive end DeMarcus Lawrence was placed on the reserve-suspended list. He will miss the first four games for violating the NFL's substance-abuse policy.
The fourth-round pick from Mississippi State finished the preseason 39-of-50 passing (78 percent) for 454 yards with five touchdowns and no interceptions. He also ran for two scores.
Tight end Rico Gathers,Cheap Football Jerseys, who is making the transition from basketball after not playing football since eighth grade,Air Max 95 Sale Cheap, was waived. The former Baylor basketball standout is likely headed to the practice squad if no other team claims him.
The addition of Sanchez gives Prescott a backup who has made 72 regular-season starts and played in two AFC championship games,Air Max 95 Sale, with the New York Jets in 2009-10. Moore has already been placed on season-ending injured reserve.
The six-year veteran was acquired by the Broncos in the offseason after Peyton Manning retired and Brock Osweiler bolted to Houston in free agency. But the 29-year-old Sanchez couldn't beat out second-year pro Trevor Siemian, a seventh-round pick in 2015 from Northwestern.
Second-year quarterback Jameill Showers survived the initial round of cuts after a marginal showing in the preseason finale against Houston, but Sanchez's arrival could change his status.
The Cowboys placed running back Darren McFadden on the non-football injury list, sidelining their leading rusher from last season for at least the first six games. He broke his right elbow during the offseason.
Sanchez reached a deal with the Cowboys the same day he was released by Denver as all NFL teams had to get their rosters to the 53-man limit for the regular season. Sanchez's release cleared him to join any team.
The Cowboys said they would be in the market for a veteran quarterback as soon as backup Kellen Moore broke his right ankle in a training camp practice. They didn't make an immediate move, though, and Prescott had strong showings in the first two preseason games.
A person with knowledge of the agreement told The Associated Press on Saturday that Sanchez had agreed to a one-year contract that could be worth $2.5 million with incentives. The person spoke on condition of anonymity because the contract can't be signed until Sunday.
The Cowboys waived a pair of former fifth-round picks in receiver Devin Street (2014) and defensive end Ryan Russell (2015).
When Romo went out unexpectedly just three plays into the third preseason game against the Seahawks, Prescott came in and led the Cowboys to a touchdown on his first full possession.

The Dallas Cowboys are adding quarterback Mark Sanchez as the backup to rookie Dak Prescott while Tony Romo recovers from a back injury.
Defensive end Mike McAdoo was placed on the waived-injured list despite a strong showing in the preseason finale,Lebron James Shoes Clearance.
Former Texas A&M quarterback Jerrod Johnson,China Football Jerseys, who signed before the preseason finale in case Showers got hurt, was among those waived.
The move on McFadden wasn't a surprise because rookie Ezekiel Elliott, the fourth overall pick in the draft, is expected to start the Sept. 11 opener against the New York Giants. Alfred Morris, a two-time Pro Bowl runner who signed as a free agent before the draft, is Elliott's backup.