Pettis (20-7) tapped out at 2:08 of the third round, after Poirier (22-5) moved to full mount with a body triangle. It was immediately clear that Pettis suffered some type of injury during the sequence.
Roufus said he was relieved that the diagnosis was a fractured rib.
"It was a unique move, Dustin had his legs on that body triangle a little higher, on the ribs," Roufus told ESPN. "We're optimistic about it. When I was 19, I suffered an injury that I still struggle with and that's torn rib cartilage. When Anthony tapped on Saturday, I was worried that's what it was.
"Bones are always easier to heal than ligaments and tendons. We're looking at the bright side of the situation."
It was a strong performance by Poirier start to finish, although there was one moment of potential controversy.
Late in the second round, referee Keith Peterson stopped the action to have a cut on Pettis' face medically evaluated. At the time he paused the fight, Pettis had Poirier in a potential triangle choke.
Pettis was eventually cleared to continue but lost the position. Roufus said the team isn't happy about it but is moving forward.
"It was wrong," Roufus said. "We could waste time trying to complain and file a grievance with the commission, but the chances of getting that overturned are slim to none.
"The angle of that triangle was one of this best triangles. It reminded me of one he hit on Shane Roller [in 2010]. It is what it is. Ironically, I told that referee in the locker room before the fight, 'You're one of the good guys.' He said, 'I hope you're telling me that after the fight.'"
A former lightweight champion, Pettis is now 2-5 in his past seven fights. Roufus said the losses have been difficult, but the Milwaukee-based team's morale will survive them.
"We're working on figuring out what's wrong ourselves," Roufus said. "We're just focused on what the next step is. He looked very well in preparations. You get in the middle of a fight, things happen, you get cut, damaged. He's fighting the best guys.
"He was a hair away from that submission. If he gets that, we're not having this conversation right now. It was an incredible fight, I think the fans appreciate that."