Former Manchester United midfielder Anderson says knee problems were the reason for his lack of first-team action at Old Trafford.
A regular under Sir Alex Ferguson after joining from Porto in 2007, the Portuguese played more than 100 games for the Red Devils and was grateful for his time in Manchester.
"I played for eight years for Manchester [and] I would like to thank the club," Anderson is quoted as saying by Sky Sports.
"In my first four years I won everything there - Champions League, Premier League and (the FIFA Club World Cup). I had a knee injury and returned to play again too fast.
"I played but the knees were not equal and I got myself injured again."
Questions have been raised over the fitness level of the 26-year-old but he insists that he is ready to train hard and secure a regular place at his new club, Sport Club Internacional.
"Do you think I'm not fit? A player will always be criticised," he said.
"I had injuries in the past, but I have to be quiet right now and answer in the field.
"It will be a pleasure play for a club such as Internacional. I want to be happy as I was at other clubs.
"I'm coming back to Porto Alegre because Inter went after me. The president gave me attention. I was training [at United] but not playing."
