Amukamara, 31, signed a one-year contract worth more than $1.18 million on May 18. He was expected to start opposite second-year corner Trayvon Mullen.
But rookie Damon Arnette, the second of the Raiders' two first-round picks, excelled in training camp. And Mullen, who missed more than a week of practice with an undisclosed issue, returned to practice Monday.
The Raiders also used a fourth-round pick on slot corner Amik Robertson, who has flashed in camp and will back up Lamarcus Joyner. Second-year cornerbacks Isaiah Johnson and Keisean Nixon also had their moments in camp. Veteran Nevin Lawson will serve a one-game suspension to start the season.
With Lawson out Week 1, Mullen (10 career starts) would be the only outside cornerback with at least one NFL start.