The 26-year-old joined his hometown club on Tuesday after several frustrating years at Old Trafford, with United allowing him to move for free despite paying ??26m for him back in 2007.
Anderson was a first-team regular for the first four years, but then fell out of favour with questions over his weight and commitment – and he spent last season on loan at Fiorentina.
Now he is hoping for a fresh start back in Porto Alegre.
Anderson said: “I played for eight years for Manchester. I would like to thank the club. 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.”
Anderson suffered several knee injuries while at United, most notably in February 2010 when he hurt his anterior cruciate ligament, ending his season.
He also faced questions regarding his weight and commitment.
Asked about that, he said: “Do you think I’m not fit? A player will always be criticised. 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.”