Advice.
Don't do it. You're getting nothing in return. Basically, you've giving up a possible #3 WR in your scoring system for what should be considered a #4-5 WR with the way SF is playing right now. You're giving up a guy you can play, for a guy that you can't. Doesn't make sense to me. I know you're WRs are pretty stacked, especially with Bryant taking punts, Mike Williams playing great as a #3, and you could afford to lose Cribbs, but that doesn't mean you take a down grade at that position for him. I think he has higher value in your scoring system than Crabtree (because of how poor he's playing). Because of your WRs, you must be lacking elsewhere in a 12 team league. Try and get a position player that can actually help you.