Oakland released Hackenberg from its 90-man roster Tuesday, three weeks after acquiring the backup quarterback from the Jets for a conditional seventh-round choice in 2019. A traded player typically must remain on his new team's roster for a period of games or past mandatory roster reduction dates for conditional choices to change hands.

New Raiders coach Jon Gruden said the decision was made to cut Hackenberg because roster spots were needed to sign veteran defensive linemen Frostee Rucker and Ahtyba Rubin.

"I was disappointed in not really giving Christian the opportunity to go to camp," Gruden said after practice Tuesday. "We felt like we needed to add a couple defensive linemen. We ran out of numbers, and that's not good at that position heading into camp."

Gruden liked what he saw from Hackenberg when the former Penn State quarterback appeared on the ESPN-produced Gruden's QB Camp two years ago. The move to acquire Hackenberg amounted to an extended tryout, with no strings attached.

The Raiders headed into their mandatory three-day minicamp Tuesday with Derek Carr, Connor Cook and EJ Manuel as their top three quarterbacks. Like Hackenberg, all three were past participants in Gruden's QB Camp, giving the Raiders coach an extended look at all of them before they entered the NFL.

A second-round pick of the Jets in 2016, Hackenberg is the third QB drafted in the first two rounds in the common draft era not to play an NFL game in his first two seasons. The last to do it was Jim Kelly, but he played in the USFL at the start of his career.

Also Tuesday, Oakland waived linebacker Brady Sheldon.