Augusto broke down during victory over Deportivo La Coruna.
Marca says the Argentine suffered a significant knee injury during the last campaign, although that occurred on the other knee to the one affected on Sunday.
After undergoing medical tests, doctors have now confirmed that it is a tear in Augusto's right knee ligament, sidelining him for 'at least six months'.
"The news about Augusto isn't good, but it's best that we leave the medical evaluation to the doctors," Atletico coach Diego Simeone explained.
"The afternoon hadn't been going well as the injuries were negative and required us to make forced changes."