Adam Schefter reports on the latest with Baltimore QB Joe Flacco's back tightness that will sideline him for a week in training camp. (1:07)

The Baltimore Ravens have signed arena league quarterback David Olson, the team announced Friday.

The Ravens desperately needed another healthy quarterback after they began training camp Thursday without starter Joe Flacco, who is expected to miss a week because of a back injury. In the first practice of training camp, Baltimore used offensive assistant coach Matt Weiss to line up under center and hand off to running backs in drills.

Flacco notified the team about his back injury just before the first full-team meeting of camp, which didn't leave the Ravens enough time to add a quarterback for the first practice. Olson will help spell Ryan Mallett, who has taken Flacco's spot with the first-team offense, and Dustin Vaughan, who is on his fourth team in four seasons.

David Olson played under Ravens coach John Harbaugh's brother, Jim, at Stanford. AP Photo/Rick Scuteri

Coach John Harbaugh had indicated Baltimore was primarily looking for someone to help the team only in the short term and said Colin Kaepernick was a possibility, although nothing was imminent.

"He's a really good football player," Harbaugh said of Kaepernick after practice Thursday. "I believe he's a really good person. It all depends on a lot of things. It depends on Colin first of all and what's his passion, what's his priority, what's he want to do, what kind of shape he's in. So we'll just see where it goes. I don't think it's different for us than any other team."

The agreement with Olson would not preclude the Ravens from adding Kaepernick.

Olson worked out for the team Thursday.

He played under Harbaugh's brother, Jim, at Stanford, where he was beat out by Andrew Luck for the starting job. He transferred to Clemson for his final season and most recently played for the KC Phantoms of Champions Indoor Football.

ESPN's Jamison Hensley contributed to this report.