"I felt like I accomplished a lot and it was time to go to the next thing," Mitchell told the Oregonian. Yahoo! Sports was the first to report Mitchell's departure.
Mitchell (6-foot, 189 pounds) led the team with five interceptions and seven pass breakups this season. In three seasons as a starter, Mitchell had a total of seven interceptions and 25 pass breakups.
Apparently that wasn't enough to sway those that looked at Mitchell's tape.
"It wasn't a fair evaluation," Mitchell said. "It came back in like a week and they didn't have time to break down film. They didn't get chance to really dissect what was real. I've been an underdog my whole life.
Oregon is still waiting to find out if All-America corner Ifo Ekpre-Olomu will also declare for the draft. If he joins Mitchell in leaving school early, Oregon would have a completely new secondary next season, as safeties Avery Patterson and Brian Jackson are both seniors.
Follow Dan Greenspan on Twitter @DanGreenspan.