I'm not 100% certain, but I think the problem with chasing Antonio is that Forest have a transfer embargo still in place i.e. - they won't be able to buy a replacement, so unless the Chairman wants to bring money in to help balance the books (or meet the FFP rules) there is little incentive to deal at a reasonable price. I think any signing they make must not cost the club a transfer fee and must cost less than £600,000 a year.
I think they also have lost 2 players to Newcastle - they were purchased last summer and loaned back to Forest... Darlo the GK, and Lascelles (def). So, unless there is a financial imperative (or a player really kicking up a stink) there is little incentive for Forest to sell.