Raiders QB Marcus Mariota on injured reserve with undisclosed injury

HENDERSON, Nev. -- The Las Vegas Raiders placed backup quarterback Marcus Mariota on injured reserve Monday with an undisclosed injury.NFL Network reported it was a pectoral injury, which would explain Mariota's accuracy issues in camp.

Per the NFL's COVID-19 rules tweaks, Mariota conceivably could return to Las Vegas' 53-man active roster in three weeks.

With Mariota sidelined, the Raiders signed DeShone Kizer to their practice squad after he spent last season on the team's 53-man roster but never played in a game. In fact, Kizer was active for three games late in the season before being demoted to No. 3 behind Mike Glennon for the season finale. He never appeared in a game.

The Raiders enter Sunday's season opener at the Carolina Panthers with Nathan Peterman as Derek Carr's backup.Peterman recently restructured his contract, going from a non-guaranteed one-year, $2.133 million deal to a guaranteed one year, $1 million contract.

It has been a disappointing start to Mariota's Raiders career following five seasons with the Tennessee Titans. After recovering from ankle and shoulder injuries this summer, Mariota had a hard time locating his passes in camp.

A source told ESPN that the previous maladies were not an issue and that Mariota should return soon. He was not on the practice field on Monday, the first practice the Raiders held with their 53-man roster and practice squad.

Mariota, 26, signed a two-year, $17.6 million free-agent contract with the Raiders in March with a base salary of $7.5 million for 2020 fully guaranteed. Not quite starter money, but big money for a backup.

The 2014 Heisman Trophy winner was expected to push Carr in camp and while his running ability was on full display and Raiders coach Jon Gruden called him a "dazzling playmaker with his feet," Mariota could never truly get his arm going.

In other moves, the Raiders also placed rookie linebacker Tanner Muse on IR and re-signed linebacker Kyle Wilber and offensive tackle Sam Young.

The Raiders have had a tough offseason in regards to money. Besides the $7.5 million guaranteed Mariota, they paid safety Damarious Randall a guaranteed $1.5 million before cutting him and also paid third-round draft pick Lynn Bowden, Jr. his $985,000 signing bonus before trading him to the Miami Dolphins.

Two of the Raiders' top seven figures in terms of cap numbers are on IR in Mariota ($9.125 million) and wide receiver Tyrell Williams ($11.1 million).

Las Vegas' other top seven cap numbers for 2020 are Carr, right tackle Trent Brown ($21.5 million each), linebacker Cory Littleton ($11.75 million), right guard Gabe Jackson ($9.6 million) and safety/slot cornerback Lamarcus Joyner ($9.2 million), per ESPN Stats & Information.