McClain, a three-year starter, hasn't played since suffering a spinal cord contusion on Dec. 9, 2012. He's been on the physically unable to perform list, but The Baltimore Sun reported McClain was cleared to return.
Harbaugh said "there is some truth" to the report. The back specialist looked at McClain's most recent MRIs and it's "very favorable," according to Harbaugh.
"I’m not in position to sit here and say completely 100 percent," Harbaugh said. "I don’t know that. There is a process that’s still involved. It’s encouraging, to say the least. It’s all positive that way."
Under PUP rules, McClain is eligible to return to practice Monday. Once he begins practicing, the Ravens have a three-week window to decide whether to activate him on the 53-man roster or keep him on PUP for the remainder of the season.
Asked whether he anticipates McClain practicing next week, Harbaugh said, "That’s something we have to decide. There will be a couple of factors that will go into that. His shape, our situation. That’s something we have to see. He hasn’t played for a long time. We’ll just have to see. I know he can by rule."