Webb is expected to have the back evaluated over the next few days. Webb hasn't practiced since Friday when he left practice early after bending over at the waist in pain.
"He's got some back things that we're looking at right now," Harbaugh said of Webb following a practice Monday night at M&T Bank Stadium "Backs are a little weird. At first, it was no big deal. It's lingering a little bit, so we'll find out what's going on with it."
Meanwhile, cornerback Chykie Brown returned to practice after missing Sunday with a tweaked hamstring.
Brown said his hamstring feels considerably better.
"I feel pretty good," Brown said. "I had to get loosened up. [On Saturday,] I thought my hammy was going to give out on me. My legs felt healthy and I was steady trying to force it. I felt dehydrated and it kept locking up on me, so they just took me out of practice and let me get treatment and rest for one day. I told them I wanted to test it out today and it felt good."
The Ravens also lost cornerback Aaron Ross for the season with a torn Achilles suffered during the conditioning test.
Brown expressed confidence that Webb will be back soon.
“We’re hopeful he’ll be back real soon,” Brown said. “We miss him out there. We’re holding it down for him. He’s working out behind closed doors and getting better with treatment.”
Several players aren't practicing, including offensive guard Will Rackley (concussion symptoms), offensive tackle Parker Graham (groin).
Defensive end Chris Canty wasn't at practice due to a "family issue," according to Harbaugh. He didn't practice Sunday when Harbaugh gave several veteran players the day off.
Nose tackle Terrence Cody is on the physically unable to perform list after undergoing offseason hip surgery. Cody is out indefinitely.