Todd Archer of ESPN reports Prescott has a latissimus strain in his throwing shoulder.
The Cowboys say the quarterback will undergo treatment, with athletic trainers and doctors evaluating him on a day-by-day basis.
Thus, it is unknown when Prescott might practice again.
“I felt some soreness when making certain throws today, and I really just decided not to push things too far,” Prescott said in a statement released by the team. “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 did not participate in team drills Wednesday, leaving for the locker room before practice ended.
The Cowboys went 2-3 in Prescott’s starts last season and 4-7 with Garrett Gilbert, Andy Dalton and Ben DiNucci starting games in his absence. Prescott’s season-ending right ankle injury happened in Week 5 against the Giants.
Dalton left in free agency, leaving Gilbert, Cooper Rush and DiNucci to compete for the backup job behind Prescott.