Best case scenario is he's healthy and has his best year. In this best case, you are now looking at his next contract at 28-30M a year. We don't need to be the team on the hook for that much money for the player he is and with his injury history.
If we pick up his option and he has a great year, we get him the next year for his $17.5 million option year. At that point we can decide if we want to keep him for the 5th year at that price or if we want to trade him then. There is no point in trading him this year when you can get so little for him and his value is at it's lowest.