Diaz was born on July 6th, 2001, in Chacao, Venezuela. When he was 16 years old, he had become an international free agent and was taken off the market by the Kansas City Royals. He was sent to pitch in the Dominican Summer League, and he appeared in a dozen games, had a 3.38 ERA, and he struck out 22 hitters in 21.1 innings.  

The right-hander stayed with the Royals up until last season, in a half decade in the minor leagues he took the bump in 61 games, had a strong 3.38 ERA, retired 149 hitters with strikes while only walking 26 in 157 innings.