Leonardo da Vinci got visual inspiration from two main sketches; one from Francesco di Giorgio and Giacomo Andrea. They both were friends with da Vinci and met with him personally around Lombardy in 1490 and discussed their sketches. Francesco di Giorgio’s sketch of Vitruvian Man features a sketched semi-turned male figure enclosed within a perfect circle centered around the genitals. Giacomo Andrea's Vitruvian Man features a male figure enclosed in a circle and a square, but the body measurements are not as accurate as Vitruvian's original descriptions.
Sources: https://commons.wikimedia.org/wiki/File:Vitruvian_Man_by_Giacomo_Andrea…
https://commons.wikimedia.org/wiki/File:Vitruvian_Man_by_Giacomo_Andrea…
Isaacson, Walter. “Vitruvian Man”. Leonardo Da Vinci. Simon & Schuster, 2017.