Ronaldo is coming to the end of his second season at Juve and still has two years left on his contract.
The 35-year-old is expected to honour his deal, but Nani believes his countryman could join him in MLS once he leaves Turin.
“A couple of years ago, he told me that he will probably end up in America,” he told ESPN.
“It’s not 100 percent but probably. There is a chance.”
The former Lazio winger played with CR7 at Manchester United and together they helped Portugal win Euro 2016.
“It is a great league,” explained the 33-year-old, who is currently on the books of Orlando City.
“Obviously there are points where we must improve as a league, even in the quality of the players.
“Here you have fantastic clubs, well organised with fantastic conditions, great coaches, great players. You see every season improving.
“I think we all have the conditions in this league. We are in a great country.
“Everything is around us. It is all about being better, not being afraid to improve.”