Max Kellerman is confident that Aaron Rodgers, with the right personnel around him, can lead the Packers to another championship. (0:59)

GREEN BAY, Wis. -- Second-year linebacker Oren Burks, penciled in as a starter in the Green Bay Packers base defense, is believed to have a torn pectoral muscle, a source told ESPN on Saturday.

More tests are scheduled to determine the course of action, another source said, but the Packers' defense has lost a starter at least temporarily.

Burks, a third-round pick in 2018, was expected to start next to Blake Martinez in the middle of the 3-4 defense. Burks played only 122 snaps as a rookie but was slowed by a shoulder injury in his rookie preseason. Burks missed the first two games of the 2018 season while recovering.

The injury occurred in the first quarter of last Thursday's preseason opener against the Texans. It was originally believed to be a shoulder injury, but the Packers on Saturday called it a chest injury.

Coach Matt LaFleur did not provide an update after Saturday's practice when asked whether Burks would miss significant time.

"Honestly, I don't really know anything right now," LaFleur said. "It's kind of wait and see, but I hope not."

The Packers used undrafted rookie Curtis Bolton in Burks' place during practice and had seventh-round pick Ty Summers working with the second-string defense even though Summers led the team with 10 tackles against the Texans. Summers also had an interception during practice off quarterback DeShone Kizer.

That inside linebacker spot, however, could be considered a part-time player because defensive coordinator Mike Pettine at times uses a safety in that position during his sub packages. On Saturday, safety Raven Greene was the first one in that spot in the dime defense, while fellow safety Josh Jones also has lined up there this summer.