Saritama pulled a leg muscle during a match for his club Deportivo Quito in a win over Liga de Quito on 15 June and the 27-year-old will not make the tournament starting in Argentina on 1 July.
23-year-old Nazareno joined up with the squad this afternoon.
"It is really sad and a shame to lose a player. It's tough on the group and for him. He is a great professional who had worked hard to be ready," coach Reinaldo Rueda said.
Ecuador's best finish in the continental tournament is fourth place, which they achieved in both 1959 and 1993, on which occasion they were hosts.
This year they compete in Group B alongside holders Brazil, Paraguay and Venezuela.