The 24-year-old has been struggling with a back injury for the majority of the season and will now require surgery to amend the problem.
Harbaugh told reporters: "I think the chances of him playing the rest of this year are probably pretty slim. There's a good chance he's going to get surgery here real soon.
"I don't want to say for sure 100% because I don't know if I'm authorized to say that, but I would anticipate that right now."
The Ravens face the Cleveland Browns on Sunday.