"He was excused for a very personal reason," coach Josh McDaniels said. "I am going to respect that and I hope everybody else does, too."
KDVR television in Denver first reported that Moss was considering walking away from pro football. Moss didn't return text or phone messages from The Associated Press.
Moss signed a nearly $15 million, five-year contract as the 17th overall pick out of Florida in 2007, but he recorded just 3½ sacks in two NFL seasons.
He was switched from end to linebacker in the Broncos' new 3-4 scheme, and after training camp opened Friday, he said: "It's a brand new start for me. I'll continue to work hard and pray and everything will take care of itself."