He started his first game for PSV in January 2009. Soon after, the 21-year-old former Brazilian U-20 national squad goalkeeper moved to Sparta Rotterdam until the end of the season. In the 2011/12 season he played at the second team. On September 28, 2011 his contract was terminated by mutual consent and Ramos returned to Brazil.
In the end of 2011, after terminating his contract with PSV Eindhoven, Cássio signed with Corinthians. On April 27, 2012, he was made Corinthians' first-choice goalkeeper, replacing Júlio César, the former number one goalkeeper at the club. He made his debut in the Libertadores 2012 on May 2, 2012, in a game against Emelec in the round-of-16. The result was a goaless draw and Cássio was elected Man of the Match following a great display. He went on to make 7 more appearances for Corinthians in the competition, helping the team being champions, including a miraculous save against Vasco da Gama in the second-leg of the quarter-finals. On December 16, 2012, Cássio helped Corinthians beat Chelsea by the score of 1-0 in the FIFA Club World Cup. He was later rewarded the golden ball for the tournament due to his brilliant performances during the competition.