The person spoke on condition of anonymity because the contract can't be signed until Sunday.
As a vested veteran, Sanchez is able to sign with any team immediately after being released by Denver, as opposed to having to go through the waiver process where teams, in reverse order of their 2015 finish, would have been able to put in claims for his services.
The 29-year-old Mark Sanchez was acquired by Broncos this offseason in exchange for a conditional seventh-round draft pick to compete with Trevor Siemian and rookie Paxton Lynch for the franchise's starting job.
The Dallas Cowboys will be losing starting quarterback Tony Romo for the first half of the 2016 regular season.
The Broncos also cut running back Ronnie Hillman, their leading rusher last season with 863 yards. He broke his right elbow during the off-season.
"Dak Prescott is expected to be the starter against the Giants on September 11", the team's website said.
It is now rumored that Kaepernick lost his quarterback job when his team chose Blaine Gabbert as their starter.
Colin Kaepernick is expected to make the final cut for the San Francisco 49ers, but a trade is still in consideration, basing on the latest National Football League rumors.
Sanchez did not play in the last two preseason games, and his salary was regarded as too steep for a third-string quarterback.
After holding off on adding a veteran following Moore's injury, the Cowboys knew they would have to add one once Romo got hurt.
Dak Prescott is going to start for Dallas, but at least the Cowboys will have a backup in place if he either struggles badly or gets injured. He tossed one touchdown and one interception. He showed promise throughout the preseason, though. Nevertheless, the whole team is comfortable with him joining the starting lineup.
The Cowboys' desperation for a back-up quarterback could end up costing them.
Safety Shiloh Keo was placed on the suspended list. Romo is expected to miss anywhere between four to ten weeks because of it.