Castellanos has been one of the most difficult players to determine a future for in the Motor City. At just 25, Castellanos is coming off the best season of his career. He seems like a prime candidate to keep and rebuild the franchise around. Indeed the Tigers thought so, reportedly offering him an extension early in the offseason.
Castellanos turned down the extension offer however, apparently choosing to explore free agency after the 2019 season. If he is not interested in an extension then the Tigers best bet is to trade him while he still has value. Indeed a report indicates that Castellanos is on the trade block.
However, a trade does not need to happen this offseason. Opposing teams are likely going to want to see if Castellanos can handle the outfield defensively before they shell out the prospects necessary to acquire the young slugger.
Plus, just because an agreement on an extension was not reached after the season does not mean that the Tigers and Castellanos will not work something out before 2019. Indeed the Tigers could increase their offer if he improves defensively in right field, where he will start next season.
Regardless, it seems unlikely that Castellanos will get dealt before the start of the 2018 season. With too many questions about his defense, and with him under team control for two more years, the Tigers will likely want to hold out and analyze if Castellanos is worth extending as a part of their rebuild. If they think he is better utilized as a trade chip, they can move him midseason or next offseason.
The trade market is very much a buyers market, with J.D. Martinez, Justin Upton and more recently Andrew McCutchen receiving very little return. The Tigers should hold Castellanos and bank on another successful hitting season and improvement on defense. If he is able to do that, they will have the luxury of either trading him for a nice haul of prospects, or shelling out an extension and rebuilding the team around him.