I'm no expert, but the fall/hit causing the injury didn't seem like it would have created a high-degree concussion. I wouldn't be surprised if he were back next week. That being said, I'm disappointing this happened as he was coming off a decent game in Week 3 where he went over 100yds from scrimmage and I was hopeful it would lead to a bigger role this week. I've been trying to sell him wherever I can the last couple weeks, but have had no success.
He's not waiver fodder unless you're in less than 12 man leagues, and he's not start-worthy until something gives (e.g. injury to Woodhead/Brown). However, he is moving his way up list of first player gone if that keeps up.