ALAMEDA — The reason for claiming DeShone Kizer off waivers became clear Monday when the Raiders placed reserve quarterback Nathan Peterman on injured reserve with an elbow injury.

Peterman, whose struggles with the Buffalo Bills in a starting role have been well chronicled, had a solid exhibition season. Coach Jon Gruden was excited enough about his progress that he never officially named a winner in the competition between Mike Glennon and Peterman to back up starter Derek Carr.

In four exhibition games, Peterman completed 71.4 percent of his passes (60 of 84) for 475 yards, three touchdowns and no interceptions while being sacked five times. Gruden said the elbow became an issue late in the exhibition finale against Seattle.

“He came over on the sideline with a sore right elbow,” Gruden said. “After the game it got a little bit more sore. Gave him an MRI and there’s a little ligament problem there. He won’t have to have surgery.”

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The Raiders were aware of Peterman’s injury Sunday when they claimed Kizer, but didn’t didn’t immediately place him on injured reserve. Instead, defensive end Josh Mauro was released. Mauro was brought back to the roster Monday, as was linebacker and special teams captain Kyle Wilber.

Placed on injured reserve was fourth-round pick Isaiah Johnson, who took a knee to the head in the exhibition opener and had what Gruden termed a “facial” injury.

Technically, Peterman could return this season after eight games if he were to be designated for return. Each team can select two players to return from injured reserve once the initial 53-man roster is formed. However, it’s unlikely a backup quarterback would be brought back without an injury to the starter.

Raiders coach Jon Gruden on Peterman’s injury, claiming DeShone Kiser pic.twitter.com/sWusQFHLDn — Jerry McDonald (@Jerrymcd) September 2, 2019

Glennon was 41 of 61 for 491 yards and and two touchdowns this preseason. He had two interceptions in the exhibition opener against the Rams and then none afterward.

The Raiders offense operates differently with Glennon, who at 6-foot-7 is less athletic and more of a traditional dropback, downfield passer. He averaged 8.0 yards per attempt during exhibitions as opposed to 5.7 for Peterman.

In Kizer, the Raiders have another project similar to Peterman in that he had some difficult moments playing for a bad team with a suspect supporting cast. Kizer started 15 games as a rookie second-round draft pick out of Notre Dame on Browns team that finished 0-16.

Traded to Green Bay before the 2018 season, Kizer played in just two games and lost the competition to be the backup quarterback to Aaron Rodgers, with the Packers opting for Tim Boyce.

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Raiders face more challenges with Patriots’ Cam Newton than they did with Tom Brady “He’s only 23 years old . . . started two games in the preseason this year for Green Bay, so he’s had a lot of reps,” Gruden said. He’s had a lot of experiences. I’m sure most of his bad experiences, like Peterman, will be reported over and over. But I think he’s got a big upside.”

Kizer, who was not made available to the media, has begun what Gruden called a “crash course” in learning the system. His job will also be the one Gruden had ticketed for Peterman — simulating mobile quarterbacks on the scout team.

“We need a quarterback that can move around and emulate (Patrick) Mahomes and DeShaun Watson,” Gruden said. “Peterman was going to do that for us, the zone reads, all the things that he’s able to do. Now Kizer gives us a dimension that will help us prepare for opponents.”