The 26-year-old catcher is eligible for arbitration for the first time this winter, and MLB Trade Rumors estimates that he will end up earning around $2.2 million in 2014. However, that number will continue to rise over Castro's next two arbitration years; if the team can't sign him to a long-term extension, then they may find him more valuable as a trade chip than as a high-priced player on a losing team.
Furthermore, the Astros are high on Max Stassi, the catching prospect acquired from the Oakland Athletics last February. Stassi had a strong year in Double-A in 2013 and ended up making his Major League debut in August. If he continues to develop into a productive player and presents a cheaper option, then Houston could choose him as its long-term plan behind the plate and deal Castro to fill needs elsewhere on the diamond.
One thing is for sure: Castro established himself as a valuable player in 2013. The left-handed batter hit .276/.350/.485 (130 OPS+) with 18 home runs in 120 games and racked up 4.5 WAR, per Baseball-Reference, en route to his first All-Star bid. He also rates as an above-average defensive catcher.
Given his skill, his young age and his remaining years of team control, he could bring back a hefty haul in a trade. Indeed, Rosenthal reports that rival teams have already begun asking about Castro. If Houston decides to keep him, then they could opt to move him to first base to make room for Stassi, especially given that Castro already has a major knee surgery on his medical resume after tearing an ACL in 2011.