Cleveland Browns quarterback Robert Griffin III, who said after Sunday's game that he sprained his left shoulder, has a "potentially serious shoulder injury," a source tells ESPN's Adam Schefter.
The possible serious nature of the injury was first reported by Fox Sports.
Griffin was undergoing tests Monday.
"The play happened, and you just got to move on from it," Griffin said. "You know, sprained shoulder. Just gotta monitor it and see how it goes."
Griffin said he "hurt pretty bad" after he was hit by cornerback Jalen Mills at the end of an 11-yard run with 3 minutes, 41 seconds left and the Browns down 22-10. He also said he was in pain as he spoke postgame.
"We'll see more tomorrow, see how my shoulder's feeling and I'll go from there," Griffin said.
The Browns said Griffin will undergo more tests on his left shoulder, which at least brings his availability into question for Sunday's game against Baltimore.
Griffin did not use his left arm a lot as he was getting dressed. At one point, he reached across his body with his right arm to take something out of his left pocket.
He finished dressing in the training room after taking his shirt in with him. Trainers also were paying close attention to Griffin after the game, which would be typical, given Griffin's description of his sprain.
"I can move my left arm," Griffin said. "I'm in pain, but I'll be OK."
Griffin had been criticized during his tenure in Washington for not sliding or protecting himself, something Browns coach Hue Jackson had demanded he do in Cleveland.
In the preseason, Griffin slid early and often, and he was praised by Jackson for doing so. But on this late scramble, he didn't head directly to the sideline or slide -- even though there was room to do both.
"I was trying to get out of bounds," Griffin said. "He kind of just surprised me there. I feel like I had done a decent job of protecting myself recently. I wanted to continue that. To get hit him that moment kind of surprised me there."
It almost looked like Griffin ran right into Mills, who had little choice but to make the tackle at the Browns 15-yard-line.
Mills said Griffin got to him quickly. "As soon as I saw him get out of the pocket, the tight end got up on me and I shed the block on him," Mills said. "Next thing I know he was right behind the blocker."
"Just an unfortunate play," Griffin said. "Just trying to fight for as many yards as we could. Try to go score a touchdown and put us in the best position to try to win the game. It hurt pretty bad."
Griffin stayed in the game as the Browns went for the first down on fourth-and-4, but he took another shot throwing incomplete to Andrew Hawkins. Griffin was examined after going to the sideline, but he did not want to leave the game. He returned for the Browns' final three offensive plays, but Jackson did not take a chance and called three runs.
As Griffin stood at the podium for his postgame news conference, his cellphone rang.
"It's my mother," Griffin said with a smile. "She's really worried about me."
Information from Pat McManamon was used in this report.
