In April 1689, Massanet accompanied Alonso De León, the governor of Coahuila, on his fourth and final expedition in search of Fort St. Louis, which had been abandoned by the French by that time. The following year, after having been named comisario for the planned East Texas missions, he assisted in the creation of Mission San Francisco de los Tejas. Later that year saw the establishment of Mission Santísimo Nombre de María, also near the Neches River. Massanet would soon leave East Texas due to a disagreement with De León over the size of the military contingent at San Francisco de los Tejas. He would return to the region in 1691, but would continue to challenge authority; one such incident involved his unwillingness to provide horses to Domingo Terán de los Ríos, the first governor of Spanish Texas, for his return voyage to Mexico.
