What are your thoughts on Serena Williams as it seems like this might be her last major tournament?
Serena Williams has been such a legend. Even when I played against her, I remember when I had my biggest success - reaching the quarter-finals at the US Open - she won the title there, her first Grand Slam title when she was 19. And that was the beginning. We all thought she's going to win so many titles, she's just physically so much better than we are, the power in her shots. When you stepped on the court, like I did against her, it was very intimidating a lot of times because she had this presence on the court, she had so much self-confidence. It was pure pressure to play against her because you couldn't be short in your shots otherwise she would hit a winner. Her served was outstanding, it's the best serve we've ever seen on the tour. Even on the men's tennis tour, she would actually be right up there on the serving scale.

It's been a phenomenal ride for Serena Williams, to be at the top of her game for so many years to be around. Now she's 40, it’s just phenomenal. I would have never thought that she was going to last that long. To me she's the best player who's ever played, and I played against Navratilova, played against Steffi Graf many times – who I am a big fan of as well, and I respect her highly - but Serena has just brought women's tennis to a different level, I think.

Caroline Garcia won in Cincinnati, Simona in Toronto while Iga Swiatek is probably not in her best form at the moment. Is the WTA Tour as unpredictable as ever and who are your three favourites for the US Open?
It's very unpredictable. Iga has lost a few matches early on, I think a couple of third round matches she's lost now in that swing in America. She's still the absolute number one, if you look at the ranking points, if you look at her ranking. In tennis, you do lose matches, you can't just win every single match. So, you have to counter her in as one of the favourites.

Of course, somebody like Carolina Garcia is full of confidence. She's had an unbelievable last few months as well, not just in Cincinnati. We know that she feels comfortable at the moment, we know what kind of tennis she can play so she can be very dangerous, I think to maybe knock on the door to win the title. Simona Halep, she knows how to win Grand Slam titles. She's done it before. And we'll see how she goes with that injury, she had to pull out of Cincinnati. But I think the women’s side is exciting.

I always keep on saying it. I don't want to know who wins the title before. I don't want to be certain about it. I want surprises and we've seen it in the past and I find that very refreshing. Remember in Wimbledon, it was Rybakina. Let's not forget Coco Gauff and Madison Keys, the two of them. They love playing in the States. So, I think it's going to be it's a good mixture. And it's once again going to be extremely exciting.

After a few tough results post Roland Garros – do you think Iga Swiatek is among the favourites for the US Open?
Yes, I think so. You have to say she has still had a phenomenal year even though she lost a couple of times in the third round now. She had that loss against Alize Cornet at Wimbledon. But in tennis, you win, you lose. Nobody can win every week, it's impossible. At the end of the day, she had shown so much consistency throughout this whole year. She's still has all this experience at Grand Slam events. You can't write her off, you still have to put her in that small circle of players who could win your title, that's for sure.

Rafa has only had one match preparation going into the US Open – is that enough?
We asked ourselves so many times that question – “Has he played enough?” before, he doesn't seem to need to play that much tennis to be able to perform his best tennis at a Grand Slam event.

I think it's hard to beat at a Grand Slam in five sets because Rafa Nadal just plays phenomenal tennis, I think we get a very good idea in the first or second round how he feels as well. He was very cautious when he claimed when he played against Borna Coric, especially on the serve you could see.

He obviously knows as well, this is the Grand Slam he could win, he could go and win this to move to 23 Grand Slam titles and gets a step ahead. Novak Djokovic can't play, so he's very aware of the situation. I think even though he probably says, “I'm not playing for the titles and I don't really think about that, I just want to be healthy, and my body is the most important thing” - he will go to the US Open and he will want to win, that's for sure. And if somebody can do it, then it's him, even though he only played one match before since he had his stomach injury.

We've seen Roger Federer back in training last couple of weeks. What are you expecting on his return?
Everybody can't wait to see him back. And the question is at the Laver Cup, is he going to play singles? Or is it just going to play doubles? One thing is for sure, he's going to play something so we'll see him in action. Don't forget, he's not the youngest any more, he's been out for a long time. He played his last match last year in Wimbledon, and things are not getting easier at that age when you are out for that long. When you play a professional match out there, you can practice as much as you want, but nothing compares to playing on high-level match that shakes your body around with the adrenaline. So, we'll see what's going to happen.

I am always worried with Roger that one day he is just going to say “Okay, that's it, I call it quits.” I don't think he's going to do a Serena, where he's going to say, “Okay, I'm going to play this and that tournament”. I would love to see him play in Wimbledon and then go and retire, but it's up to him. It's a very personal decision. I think he just wants to give his knee a bit of a test, but we can't fool ourselves that he's 40 years of age and his career is coming to an end – it’s impossible to play much longer.

Barbara Schett will be working as an expert for Warner Bros. Discovery's coverage of the US Open, which starts on Monday 29 August. Watch the US Open LIVE across Europe (ex UK&Ire) on discovery+, Eurosport and Eurosport App.