Valentín Mariano José Castellanos Giménez (born 3 October 1998) is an Argentinian professional footballer who plays as a midfielder for Major League Soccer side New York City.
Castellanos started his club career at Universidad de Chile before moving to Torque in 2017. On 27 July 2018, he joined Major League Soccer side New York City on loan until the end of the 2018 season. In his first match with New York City, he started for the club and scored a goal against the Vancouver Whitecaps.
New York City exercised their option to buy Castellanos on 29 November 2018, ahead of the 2019 season.