Andre Ward says "anything is possible" regarding a move up in weight which could see him meet WBA and IBF heavyweight champion Anthony Joshua.
Ward defended his WBO, WBA and IBF light-heavyweight titles against Sergey Kovalev in a rematch on Saturday.
His coach Virgil Hunter has talked up a move to cruiserweight or heavyweight and backed the American to beat Joshua.
"He's the heavyweight champion and the man but that's just my coach's belief," Ward, 33, told Eyes On Events Radio 5 live.
"Anything is possible. Virgil will speak his mind and I will back him up. That's no disrespect to Anthony Joshua.
"Cruiserweight and heavyweight is definitely an option. Is it easy? Absolutely not. Is it a risk? Absolutely. Are people going to think you're crazy? Absolutely."
Ward held world titles at super-middleweight before claiming all but one of the recognised belts at light-heavyweight and said he would meet WBC title holder Adonis Stevenson "if there is enough buzz and people want to see it".
He added that he did not want to fight at cruiserweight or heavyweight regularly, saying: "Ideally you want it to be for a title, to make history and move on."
Britain's Tony Bellew - the WBC champion at cruiserweight - could therefore be an option and would ultimately require less of a weight jump than a contest with Joshua.
In beating Kovalev, Ward weighed in at 175lbs - around 24lbs lighter than Bellew scaled when capturing his title in 2016 and 75lbs less than Joshua prior to his win over Wladimir Klitschko in April.
"I've shown we are willing to fight the best," added Ward, who has won all of his 32 fights. "I'm coming up to 13 years as a pro. You want meaningful fights.
"The situation at heavyweight or cruiserweight, it wouldn't be to try to match them size for size.
"I'd not try to get to the maximum of 200lbs at cruiser, I'd come in at 188-190, understanding I'm the smaller man and that I'd have to use my ability."
If Ward were to win a world title at heavyweight, he would emulate Roy Jones Jr, who moved from light-heavyweight to heavyweight to take the WBA title from John Ruiz in 2013.
Jones won that title despite weighing in 34lbs less than his 226lbs opponent.