Former MK Dons midfielder Keith Andrews is to take up a full-time coaching role with the club this season.
Midfielder Gary Deegan has signed a new one-year deal at Southend.
Bayer have reached an agreement with Club World Cup winners Corinthians for the sale of the 24-year-old, who arrived in Germany in 2008 from Flamengo and made a total of 101 Bundesliga appearances, the last coming in the 3-0 win over Hamburg last weekend.
"Renato has given us plenty of wonderful footballing moments during his time in Leverkusen," the club's director of sport Rudi Voller said.
"Even if it was tough for him in recent months due to different injuries, we will always have good memories of him and he has made a big contribution to the positive development of our club."
Leverkusen's general manager Wolfgang Holzhauser revealed that homesickness had also played its part in the player seeking a return home.
"Renato is a Brazilian through and through and he missed his home country," he said. "We believe that a new beginning for him in Brazil makes sense in view of the 2014 World Cup and that he can really become an alternative for the national team over there.
"We wish him all the best."