Rafael Nadal is tennis' "greatest fighter ever", says his US Open semi-final opponent Matteo Berrettini.

Spaniard Nadal, 33, faces Italian 24th seed Berrettini on Friday for a place in the final at Flushing Meadows.

Bulgaria's Grigor Dimitrov plays Russia's Daniil Medvedev in the first semi-final on Arthur Ashe Stadium from 21:00 BST.

"It's unbelievable what he's doing," 23-year-old Berrettini said of 18-time Grand Slam champion Nadal.

"I admire him, the way he is on the court. His attitude is something that is... I think it's close to perfection.

"I think he's the greatest fighter ever in this sport."

Three of Nadal's 18 majors have been won in New York and he is a heavy favourite to close within one of Roger Federer's record men's tally of 20 Grand Slam singles titles.

He has dropped only one set in the tournament so far, against 2014 champion Marin Cilic in the fourth round.

Friday's match will be the first meeting between Nadal and Berrettini, with the latter playing in his first Grand Slam semi-final.

Berrettini defeated 13th seed Gael Monfils to progress to the last four and Nadal - who last won the US Open title in 2017 - expects a challenge.

"He is having a great year. He's in the semi-finals, winning a lot of good matches," said the second seed.

"In the semi-finals of a Grand Slam match you can't expect an easy opponent. You can't expect an easy match.

"He's serving huge, big forehands, moving well, and big confidence because he's having a great year."

Berrettini was just nine when Nadal won his first Grand Slam title - at Roland Garros in 2005 - and says his first memory of the Spaniard is from that year's Italian Open.

Nadal beat Guillermo Coria in a five-set epic to win in Rome, but, back then, Berrettini had very different priorities.

"They were showing the match on the TV for free, but it was a channel that was about cartoons," he said.

"I was young. These guys, I mean, six hours. Come on! I want to catch my cartoons."

Medvedev 'working to be better' after discipline issues

Before Nadal and Berrettini take to the court, fifth seed Medvedev faces unseeded Dimitrov in their first meeting since 2017.

Medvedev, 23, has been in the headlines for a variety of reasons in New York, facing jeers from the crowd after his third and fourth-round victories.

He was fined $9,000 (£7,400) for a visible obscenity and unsportsmanlike conduct during his third-round win over Feliciano Lopez.

"What I got I deserved. Usually I'm not like this, as I was in the third-round match. I'm not proud of it. I'm working to be better," Medvedev said.

"Hopefully I can show the bright side of myself."

Medvedev entered the US Open following a successful few weeks on the hard courts, winning in Cincinnati after reaching the finals of both the Rogers Cup and the Citi Open in Washington.

"I am surprised. That's what I've been working for all my life. That's where I've been going step by step," he added.

"I was improving my rankings. But I am still really surprised with the way this last four weeks have been going.

"That's what I've been working for. That's what I've dreamed of. I've achieved some of what I've dreamt."

'I don't want to go there anymore' - Dimitrov enjoying return to form

Until now, this has been a year to forget for Dimitrov with a shoulder injury a big factor in the former world number three slipping to 78 in the rankings and forcing him to withdraw from four tournaments.

Coming into US Open, Dimitrov had lost seven of his previous eight matches. But his five-set victory over five-time US Open champion Roger Federer in the quarter-finals demonstrated a resurgence in form as the 28-year-old reached his first Grand Slam semi-final since the 2017 Australian Open.

"It was that low that I don't even want to go there any more. It was just obviously injury, losing points, ranking. That's the lowest point of any player," said Dimitrov.

"I think the past six, seven months have been pretty rough for me. But I had somebody to lean on, my friends, my family. I kept on believing again in the work, the rehab I had to put behind my shoulder, the exercise, the practice, fixing up the racquet a little bit. There were so many things I had to adjust in such a small but big period of time.

"Next thing you know, you're almost end of the year, you have a result like that. It's pretty special to me."