Perriman sprained his knee July 30, the first day of training camp, and he hasn't practiced since. He wore a brace on his right knee while watching the joint practices with the Philadelphia Eagles last week.
It's looking like Perriman will miss the entire preseason of his rookie year.
Asked if there was an update on when Perriman would be back, Harbaugh said, "I'm asking, too. It's just slower healing than they expected."
Perriman was selected with the No. 26 overall pick this year and was expected to replace Torrey Smith as the team's top deep threat. He averaged 20.9 yards per catch and 33.1 yards per touchdown at Central Florida last season.
Ravens quarterback Joe Flacco acknowledged it's disappointing that Perriman has missed so much practice time.
"It's going to be up to him to get out there and do that as quick as possible," Flacco said. "When you're dealing with guys that are pretty talented, it doesn't take a ton of time to get in sync with one another. But, obviously, you would like as much time as possible."
With Perriman sidelined, the Ravens will likely start Steve Smith and Kamar Aiken at wide receiver. Marlon Brown is the No. 3 receiver right now because Michael Campanaro has been sidelined with a soft tissue injury.
The question with Perriman is how long it'll take for him to get up to speed when he is cleared to come back. His game is based on stretching the field. He ran the 40-yard dash at his pro day in 4.24 seconds, which is faster than anyone at this year's combine.
"I think he's an awesome talent, and he's going to help us out a lot," Flacco said. "But he's not going to help us out if he can't run. When he does get out there, I think we'll be able to rely on him."