Willis, who suffered the injury during a drill, only participated in individual drills as the team's trainers ease him in slowly.
Willis said he wanted to return far sooner.
"If it was up to me, I would try to go the next day I hurt it," Willis said. "But I didn't want to let my pride and ego hurt the team."
Among other things, Willis needs time to practice with the radio coaches want him to wear inside his helmet this season so he can communicate with defensive coordinator Greg Manusky. Willis experimented briefly with the radio last year, but then relinquished it to veteran safety Mark Roman. Roman has since lost his starter's spot.
"I want the headset," Willis said. "I break the huddle, I call the play, it's my show to run."
Even though Willis has missed time, he has nonetheless been a daily presence at practices, ducking into huddles, calling defenses and watching even the second- and third-team units.