The Raiders re-signed Bryant on Wednesday, giving the talented wideout a one-year deal after they released him on Sept. 1.
NFL Network's Ian Rapoport and Mike Garafolo reported at the time Bryant was facing another suspension from the league.
Schefter noted Bryant's camp is "confident" he has a chance to win the appeal, which was one of the reasons the Raiders decided to bring back the 26-year-old.
Oakland acquired Bryant from the Pittsburgh Steelers in April for a third-round draft pick. The former Clemson star was suspended for a minimum of one year in 2016 for violating the NFL's substance-abuse policy.
Bryant appeared in eight games with the Steelers last season after the NFL conditionally reinstated him. He finished 2017 with 603 receiving yards and three touchdowns on 50 receptions in eight games.