Russian Daniil Medvedev is the most likely player to break the Grand Slam stranglehold of the "big three" when the Australian Open starts in Melbourne next week, according to John McEnroe.
The 23-year-old's quirky style propelled him to four titles and a Tour-leading 59 match wins in 2019 and McEnroe says he provides different challenges to the old guard.
"These younger players need to accept that they need to keep adding to their game, doing something different," said McEnroe, who will be part of ESPN's coverage team.
"That's why Medvedev has had the success, because he's thrown a curve ball at these top guys that they weren't anticipating, almost like he was going back to the 12 or 14 and unders and pushing the ball.
"No one expected to see that from him. It's been a very effective tool mentally to me."
Medvedev reached the US Open final last year and pushed Rafael Nadal to the limit after a stunning fightback from two sets down.
That final showcased the Russian's dexterous game to the full, combining an incredible ability to soak up punishment before counter-attacking with searing power.
His run to the final at Flushing Meadow was quite a rollercoaster as he not only took on opponents but gave the boisterous New York crowd a run for its money.
In one match on the Louis Armstrong Stadium against Feliciano Lopez he was booed by the crowd, then showed them the middle finger, before 'thanking' them for their hostility in an on-court interview, saying he fed off their energy.
"That's one of the gutsiest things that I've seen, when he was embracing the booing, and that type of stuff. That took a lot of cojones, as they say," seven-time Grand Slam champion McEnroe said.
Even at the start of the final against Nadal, some of the crowd were unforgiving of Medvedev, but by the end he had won them over with a courageous battle against the odds.
Nadal's win meant the last 12 Slams have been won by either himself, Novak Djokovic or Roger Federer while a log jam of rising stars forms behind them.
Medvedev will be seeded fourth in Melbourne and is a possible semi-final opponent for Nadal.
"You've still got to put those guys ahead of the other guys. They just know how to get it done," McEnroe said.
"But Medvedev to me is the guy that has the best chance of winning it right now. He showed a gear that we haven't seen at the U.S. Open."