Juan Muñoz was not present at the 1540 muster. Only later in 1547 do we learn that a certain Miguel de Santiago wanted to go on the Expedition, but fell sick. So in his stead he sent Juan Muñoz, who died at some point while in Tierra Nueva. The historian fray Antonio Tello wrote in the 1600s that Juan was a vecino of Culiacán, which may connect him to the members of Nuño de Guzmán's conquest of Nueva Galicia in the early 1530s. If he was with Guzmán, then according to Tello, Juan was from Utrera in the Sevilla province.
1530-1540:
?López-Portillo y Weber, La Conquista de La Nueva Galicia [p.136];
?Garmendia Leal, Fundadores [p.104: soldados de Nuño de Guzmán, 1529, listed among the jinetes y peones];
?Tello, Libro Segundo [p.136: 1531-de Utrera en Sevilla, vecino and conquistador of San Miguel de Culiacán];
Tello, Libro Segundo [p.443: 1542 a Juan Muñoz, vecino of Culiacán, was in custody and possibly returned with Vázquez de Coronado (not correct about his return)]
1540-1550:
AGI, México, 1064, L.1\1, “Informes” [fol.270v] = Icaza, Diccionario, #1302 [Miguel de Santiago native of Alcáçar de Consuegra; son of Francisco de Santiago and María de Montoya Ramírez; came to Nueva España in 1527; in the war of Yopelçingos and Motín; worked in the conversion of the natives y evito muchas ofensas que se hacian a dios nuestro señor y quando lo de Cíbola queriendo yr aquella jornada a servir a su magestad adoleçio y envio un honbre a su costa y le dio armas y cavallos y sesenta pesos cada año que se decia Juan Muñoz el qual murio alla e que sirvio en la ultima pacificación de Jalisco y yendo a este efecto cayo un cavallo con el y le quebro un braço y siempre ha tenido sus armas y cavallo y vive en gran trabajo y necesidad]
Other info: ?AGI, Pasajeros, L.1, E.4079 = Boyd-Bowman, Indice geobiográfico, II:9779 [son of Fernando Muñoz and Juana Gómez, native of Sevilla, to Indies 1534];
?AGI, Pasajeros, L.2, E.4788 = Boyd-Bowman, Indice geobiográfico, II:9781 [son of Antón Muñoz and Ana Gómez, vecinos of Sevilla, to Indies 1538]