Jackson returned to action on Monday.
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 initially gave another reason for Jackson's absence when he surprisingly didn't practice on 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 MVP after leading the league with 36 touchdown passes and setting the NFL 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 other quarterback in NFL history. He started 15 games before sitting out a meaningless season finale.
Pro Bowl cornerback Marcus Peters also is dealing with a soft-tissue injury and has been sidelined the past two practices, Harbaugh said Sunday.