Veteran WTA coach Eric van Harpen is keeping an eye on a group of Grand Slam champions who he believes could win many more major titles.
“Garbine Muguruza, Ash Barty and Bianca Andreescu have a chance to win five Slams, but [Sofia] Kenin and Andreescu, or Osaka, they came up very young, and it's always easier to come up than to stay as a top player," Van Harpen tells TENNIS.com. "The locker rooms are not sleeping and the tension will not be easy. I think we will have more surprising winners.”
The Dutch coach has worked with several top WTA players, including Conchita Martinez, Arantxa Sanchez Vicario, Maria Sharapova, Ana Ivanovic and Andrea Petkovic.
He calls the ability to adjust against different opponents an important part of being a champion.
“They all have some opponents they do not like, such as Muguruza—she is 0-4 record against [Andrea] Petkovic, but she has a chance because with Conchita [Martinez], she has a coach who really understands the game," he says. "I like Ash Barty the most at the moment."
But consistency can be difficult to achieve—take Sloane Stephens, who has slipped to No. 37 since winning the 2017 US Open.
“I thought a few years ago that Stephens would be a candidate to follow Serena, but that was very disappointing," Van Harpen says. "It was impressive Andreescu won the  US Open, but what kind of injury she had that took her so long to come back."
And there could be even more unpredictability as players return to the tour from a five-month break, he adds. Some could go from not playing to playing too much, especially with the French Open just two weeks after the US Open.
“You think they had such a nice long rest that they all should have charged the batteries, but we have seen in the new soccer season that they had a lot of injuries,” he says. “For some of them they could recover from injuries and some of them have worked hard to get in better shape.
"I think a biggest problem will be the tournament schedule, because to play two Grand Slams in a row on completely different surfaces will be a challenge. Some players will find their rhythm and timing, because they all need match practice.”
Having watched a lot of matches during his long coaching career, van Harpen has a few favorites.
“I liked very much the 2005 Australian Open Final between Sharapova and Serena," he says. "Another match was Sanchez against Steffi Graf, 1995, because there was one game that took 20 minutes and where everything could happen to win.
"And also, Martinez won the 1994 Wimbledon, upsetting Martina Navratilova.”
Currently in Mallorca, van Harpen has been working with 21-year-old Marta Paigina for the past five years. The Russian is currently ranked No. 288, and reached the French Open junior semis. But two years ago, she injured her shoulder.
“Nobody can tell us what exactly the problem is, but she seems better now," Van Harpen says.
The WTA tour is currently scheduled to restart in two weeks in Palermo, using a protected ranking system.