"He’s not fully back. He may not be back all season long," Schefter said Friday during ESPN's broadcast of a preseason game (h/t Mike Florio of ProFootballTalk).
Prescott has been dealing with a right latissimus strain suffered during training camp that has limited him in practices and kept him out of preseason games.
Head coach Mike McCarthy said this week there is a "good chance he probably won't play" in the preseason as the team prepares for the Sept. 9 opener against the Tampa Bay Buccaneers.
Prescott is also coming off an ankle injury that ended his 2020 season after just five games.
The 28-year-old has been a star when healthy, earning two Pro Bowl selections and tallying 4,902 passing yards and 30 touchdowns in 2019, his last full season. Last year, he was averaging an incredible 371.2 passing yards per game before his injury.
It was enough to earn a four-year, $160 million extension in the offseason.
The quarterback does believe he will be able to play during the regular season and wanted to compete during the team's joint practice with the Los Angeles Rams last week.
"I felt like I could go out here, especially when you had the crowd going and the excitement, your adrenaline's rolling and you hate missing a day like this," Prescott said, per Tom Pelissero of NFL Network. "But I feel great and I'll be ready when it really matters."
The Cowboys don't have much in the way of experienced backups, with Garrett Gilbert sitting No. 2 on the depth chart.