1) He's a 10-5 guy, so he goes no where without his consent. That will mean ponying up more $ to buy said consent.
2) He's been hurt for 1 1/2 years. Who is going to chance that, even at a below market contract? Any trade would involve the Sox paying a lot of his contract, which sort of defeats the purpose of the trade.
Bottom line, trading him probably costs MORE than his current contract.