A lock forward, Vallejos started his career at Logaritmo Rugby Club in Rosario, before moving to Italy to play professionally for Overmach Parma. Vallejos Cinalli signed for English side Harlequins during the 2009–10 season to fill the gap left by the injured Jim Evans. He was a replacement for Harlequins in their 2011–12 Premiership final victory over Leicester Tigers. In June 2012 Vallejos joined the Welsh regional team the Scarlets. He was granted a release from his contract with Scarlets to allow him join the Pampas XV and compete fully in the 2013 Vodacom Cup.