Juan Cruz Guillemaín (born 21 August 1992) is an Argentine rugby union footballer who plays as a lock for the Argentine Super Rugby side Jaguares and the Argentina national rugby union team.
Cruz started his career playing for his local club, San Juan, before heading to Europe in 2012 to sign for Parisian side Stade Français along with compatriot Lisandro Gómez López. He made his Top 14 debut during the 2012-13 season, however his appearances for Stade had largely been limited to the European Challenge Cup since then.
Cruz was a member of the Argentina Under-20 side which finished 4th in the 2012 IRB Junior World Championship, he also represented the Argentina Jaguars side in 2012 and 2014.
He made his senior debut for Los Pumas on 8 November 2014 in a 41-31 defeat to Scotland in Edinburgh.