The Raiders placed cornerback Trayvon Mullen (foot), defensive tackle Johnathan Hankins (knee) and defensive tackle Bilal Nichols (knee) on the physically unable to perform list for the start of training camp, the team announced.
The Raiders can activate the players back to the 90-player roster at any point, but Mullen, Hankins and Nichols cannot practice until activated.
Mullen, a 2019 second-round pick, was limited to five games last season because of a toe injury.
Hankins ended the season on the injury report with back and knee injuries. He missed Weeks 16 and 17 and played only 29 snaps in Week 18 and 37 in the playoff loss to the Bengals.
Nichols signed with the Raiders this offseason after appearing in 60 games with the Bears the past four seasons.
The Raiders also announced they signed free agent receiver Isaiah Zuber.
Zuber joins the Raiders after stints on the practice squads for the 49ers, Browns and Jets in 2021. He entered the league as an undrafted free agent in 2020, signing with the Patriots.
Zuber has appeared in four career games and totaled two receptions for 29 yards, with two rushing attempts for 21 yards.