However, the ex-Chelsea boss also claimed Totti was "the best player" he has ever worked with.
Ranieri left Roma in February after the club suffered a dip in form and the 59-year-old, who has also managed the likes of Valencia, Atletico Madrid and Juventus, told Gazzetta dello Sport he believes Totti could have achieved more in his career if he had applied himself better.
He said: "Whether I think he's lazy? I have to agree with that yes. Nevertheless, he is the best player with whom I have ever worked.
"I have also worked with [Frank] Lampard and [Alessandro] Del Piero, but Francesco is the better player. The difference is that the other two have a better attitude. They always were very dedicated on the training pitch and were the last ones to leave the ground.
"Totti was exactly the opposite and was the first one gone."
Totti, 34, has made his first appearance in a Roma shirt back in 1993 and has made over 600 appearances for the club, but Ranieri also revealed he felt a move abroad would have suited the forward.
"He could have won several Ballons d'Or had he left Roma for Barcelona or Manchester United," he said.