He could still return this season, however.
Zbikowksi has a bulging disc in his back, and he might be able to play through it over the next couple weeks, according to head coach John Harbaugh.
"It's something that we think he's got a chance to play with," Harbaugh said. "He doesn't have anything radiating into his legs, so that's a very good sign. There might be a little bit of a ligament strain in there that we treated with some cortisone this week.
"We think we've got a chance to get him back, we just have to see how it responds to that."
As a result, the rookie is almost certainly not going to play against Cleveland this weekend.
"David hasn't cleared the concussion thing yet," Harbaugh said. "We just keep testing him. Those things you just never know."