"Derek let me know a few weeks back that he wasn't sure if he could be committed and wanted to still think about it," Bills general manager Brandon Beane said, per the team's official website. "So I knew going into the draft that this was something that could potentially happen. But it wasn't definite.
"We talked this week, and he let me know today that he is going to retire."
Anderson's last season was spent in Buffalo, where he started two games in place of injured rookie quarterback Josh Allen.
While the 35-year-old lost both games he started, his main role in his short time as a Bill was to mentor Allen, who he spoke highly of to Nick Wojton of USA Today's Bills Wire days after signing with Buffalo in October:
"I've seen a lot of football, I’ve been through a lot of ups and downs in my career and just be a guy that he can lean on. [Allen can] ask me any question. I said, 'Bud, I’m here for you, if you need me to watch a guy or find something special or something you’re unsure of’ and things like that.
"Obviously, in the last seven years I was with Cam (Newton); I watched him grow. I got real happy when I watched something during the week and point something out and he would execute it. It’s fun for me.”
Anderson began his career as a sixth-round draft pick of the Baltimore Ravens in 2005 out of Oregon State, but he took his first NFL snaps for the Cleveland Browns from 2006-09. His seasons as a Brown proved to be the best of his career.
His most productive campaign came in 2007 with 3,787 yards for 29 touchdowns and 19 interceptions. The Browns posted a 10-6 record behind Anderson that season and haven't won more than seven games since.
Following Cleveland, Anderson spent the bulk of his career with the Panthers from 2011-17 purely in a backup role to Newton.