A source told ESPN's Adam Schefter on Saturday that Griffin suffered a hairline fracture in his right thumb and is expected to be out four to eight weeks.
Griffin hit his right thumb on outside linebacker Tim Williams' helmet toward the end of Saturday night's practice at M&T Bank Stadium. The veteran QB threw his helmet on the sideline in disgust.
"I got a little issue with my thumb," Griffin said. "I hit on the helmet of one of the defenders. I guess that's why they tell them to stay away from us."
After getting an X-ray, Griffin returned to the field, where he wiped away tears while his wife consoled him. He was able to sign autographs following practice, but he needed help in the locker room to remove his jersey and shoulder pads.
Griffin later tweeted: "Everything you have been through will make you stronger."
Answering a question about whether he was concerned about Griffin, Jackson's voice started to break up.
"Definitely," Jackson said. "That's my brother."