An MRI confirmed that Brees did not suffer a serious shoulder injury this past Sunday, revealing a bruised rotator cuff with no tear, league sources told ESPN Monday.
But Brees' status for the 0-2 Saints' road game against the Carolina Panthers remains uncertain.
Brees will get a second opinion from orthopedic specialist Dr. James Andrews with another look at the MRI, and his availability will be determined by how the injury responds to treatment over the next few days, the sources said.
The timing couldn't be much worse for a Saints offense that was struggling to find any rhythm even with Brees on the field.
Veteran Luke McCown would almost certainly replace Brees as the Saints give rookie third-round draft pick Garrett Grayson more time to develop. Grayson worked mostly as the fourth-string quarterback during the preseason.
But he admitted that the soreness affected him for the rest of the game, especially on a few deep throws that "didn't come out really well," including an underthrown interception early in the third quarter.
Brees was not wearing any sort of wrap or ice on the shoulder when he was in the Saints' locker room Monday morning, but he isn't scheduled to speak to reporters until Wednesday.
"It's not gonna be something where it's long-term. I think both he and the doctors are all optimistic," Saints coach Sean Payton said Monday night on the WWL Radio coaches show, without offering any specific diagnosis. "A lot of it is gonna be on the treatment and his ability to come back and really feel like he's got the strength he needs.
"He's someone, you know as well as anyone, he's gonna be a competitor. He's gonna be smart about it as well. But I think we'll have a better idea come Wednesday."
Brees expressed confidence on Sunday night that he would be OK, though that was before the MRI was taken.
"That's the season. Everybody's dealing with something," Brees said Sunday night. "Just gotta get a little stronger, that's all."
Brees has never missed a regular-season game due to injury in his 15-year career -- he suffered a major shoulder injury in 2005, when he was with the San Diego Chargers, but that was in Week 17.
Brees revealed Sunday night that he also battled through a shoulder issue late last season.
He also played through a sprained MCL in his knee in 2010 and suffered an oblique injury in the 2014 preseason.
Payton said Brees has been "throwing it outstanding" this summer and said he is not worried about Brees' ability or performance.
"But certainly when he takes a shot like he took yesterday, and I didn't see it until watching the film today, you want to make sure he's healthy and he's upright," Payton said. "He takes that shot, and obviously that can affect you once you get hit like that. So we've gotta be better in protection. Too many times he was getting hurried."
Information from NFL Insider Ed Werder and ESPN senior NFL analyst Chris Mortensen was used in this report.