The Brazil international was unveiled as Orlando's first designated player earlier this week, following the termination of his contract at Milan.
With the new MLS campaign not due to start until next year, the playmaker will have a stint on loan at first club Sao Paulo to maintain his fitness.
MLS has often been viewed as inferior to the major divisions around Europe, with some critics seeing it as nothing more than a place for famous veterans to make money before retirement.
But Kaka refutes such suggestions, and feels he has work to do to get in shape before the season begins.
"I will do my job [but] I have to do some special physical things to be ready," he said.
"The six months [off] at the start was a problem but I'm going back to play in Sao Paulo - where I began my professional career.
"The MLS has a great future and the Orlando City project is a serious one that I'm happy to be a part of.
"I hope the MLS can grow to be among the top five leagues in the world.
"The MLS isn't where players go to at the end of their career. It can become where they go before that - [David] Villa [who has signed for New York City] has moved and now I have too."
