OWINGS MILLS, Md. -- Baltimore Ravens quarterback and reigning NFL MVP Lamar Jackson has missed the past two training camp practices because of a groin injury, sources told ESPN's Adam Schefter.

Jackson is slated to return to action Monday, sources said.

After Sunday's practice, coach John Harbaugh described Jackson's injury as a "soft-tissue" one but wouldn't expand beyond that.

"It's training camp and we're getting close to the season," Harbaugh said. "We're not talking about injuries too much."

The Ravens open the regular season in three weeks, when they host the Cleveland Browns. Robert Griffin III has been filling in for Jackson the past two days.

The Ravens initially gave another reason for Jackson's absence when he surprisingly didn't practice Saturday. Assistant head coach David Culley said Jackson was getting a day off to rest his arm.

When asked Sunday if a tired arm classified as a soft-tissue injury, Harbaugh said, "No, I'm not getting into all that. You guys are sleuthing it out and playing Dick Tracy."

Last season, Jackson became the second unanimous NFL MVP after leading the NFL with 36 touchdown passes and setting the league mark for rushing yards by a quarterback with 1,206. He became the first player in league history to produce more than 3,000 yards passing and 1,000 yards rushing in a single season.

Jackson was durable last season even though he ran the ball more than any quarterback in NFL history. He started all 15 games before sitting out a meaningless season finale.

The Ravens return to the practice field Monday morning. Pro Bowl cornerback Marcus Peters is also dealing with a soft-tissue injury and has been sidelined the past two practices, Harbaugh said.