A team spokesperson said Prescott felt the soreness early in practice and "did not want to push it," but he was not concerned about it. The ensuing examination was termed "purely precautionary," and an MRI showed Prescott has a muscle strain in his right shoulder. He will be treated and further evaluated on a day-to-day basis, the team said in a statement later Wednesday.
"I felt some soreness when making certain throws today, and I really just decided not to push things too far," Prescott said in the statement. "Better to be cautious and smart about it. I don't see this as any kind of serious setback. We'll treat it on a daily basis, and I'll be fine."
Prescott went through his normal work in the early portion of practice and did not appear to have any issues. When the Cowboys moved to one-on-one work, he spoke with head athletic trainer Jim Maurer, who tested the quarterback's strength.
Prescott told Garrett Gilbert to take more of the one-on-one snaps, and coordinator Kellen Moore told him he had the rest of the 11-on-11 drills. Prescott watched a few more portions of practice before heading to the locker room for more examination.
"It's part of being a backup quarterback," said Gilbert, who started one game last year after Prescott was lost for the season. "You've got to always be ready to step in at any point. That's all it was today, an opportunity to step in there and get some reps with the one."
In the first four practices of training camp, Prescott unofficially completed 50 of 78 passes in team drills. He was intercepted three times on Tuesday.
"He told me and Blake [Jarwin] at some point, 'Hey, I'm going to do in and do my treatment stuff and make sure this is all right,'" tight end Dalton Schultz said "I mean, Garrett does a great job in getting us going. Next man up, so I'm glad he was able to step out and do what he needed to do. It's like the second week of training camp. You don't need to be out there throwing with a sore arm."
Prescott has had no issues with his surgically repaired right ankle that he injured last October. He said he did not think once about the ankle following the first practice, and he has not shown problems running and moving in any direction.
Despite the injury, the Cowboys signed Prescott to a four-year, $160 million contract in the offseason that included $126 million guaranteed. They looked at free-agent veterans, including Jeff Driskel and Brett Hundley, but have continued with Gilbert, DiNucci and Cooper Rush as their quarterbacks behind Prescott.
The Cowboys have said they want to get Prescott some work in preseason games, which start Aug. 5 against the Pittsburgh Steelers in the Hall of Fame Game. How this injury impacts that decision is not clear, but Gilbert said Prescott was off to a good start in camp.
"It's been fun to watch him. I said a lot in the spring, just having him out there, he's been in this offense for what, five years now? Just being able to pick his brain about how he operates the offense has been great, and then getting to see him actually operate it on 11-on-11 stuff has been a lot of fun for me," Gilbert said. "That's not even to mention his leadership is probably his best quality. Watching him on a day-to-day basis and the way he brings the energy, brings the juice every day has been great for me."