There are only two mentions in the documentary record of an individual with a name close to the expeditionary's. Therefore, Juan de Vallera is probably the person present at the 1540 muster as a footman. If correct, then Vallarra was a native of Villar del Pedrosa (Cáceres province) and the son of Alonso Sánchez de Mateo and Isabel González.
?AGI, Pasajeros, L.2, E.2954 = Boyd-Bowman, Indice geobiográfico, II:3274 [September 7, 1536, Juan Vallera, son of Alonso Sánchez de Mateo and Isabel González, vecinos of Villar del Pedrosa, to México 1536]) (Vallera); [the apellido may be incorrect since there are no matches]
1540, Feb: Muster in Flint & Flint, Documents, Document 12 [sword, dagger, round shield, native arms, footman]