What's wrong with Rafael Nadal? And can he get back to his best?

    (CNN)Rafael Nadal has suffered head-shaking upsets at Wimbledon before, so in isolation his defeat to Dustin Brown in the second round last month wouldn't seem overly problematic.

    The most recent loss at the All England Club, however, came on the heels of the Spaniard losing at the French Open for the first time in six years. And in January at the Australian Open, Tomas Berdych stunned Nadal in the quarterfinals after he had fallen to the 14-time grand slam winner on 17 straight occasions.
    All this while the injuries that have so often troubled Nadal are thought to be absent.
    In the past, grand slams have been where onlookers have seen Nadal at his finest, the combination of spin, fitness -- and heart -- consistently seeing off his rivals.
    Not this year, which has begged the question, "What's wrong with Rafa?"
    If Nadal doesn't win the U.S. Open, which starts in three weeks, it would mark the first time since 2004 he hasn't claimed at least one major in a calendar year. Nadal, who turned 29 in June, won a modest clay-court tournament in Hamburg, Germany on August 2 but begins his hard-court preparation this week at the Masters level Rogers Cup in Montreal.
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    A former U.S. Open champion, Andy Roddick, for one, thinks Nadal won't end his 2015 malaise at Flushing Meadows and went even further by telling the BBC that he "probably won't win another slam" in his career.
    Now, two of the game's most successful coaches, Larry Stefanki and Nick Bollettieri, are adamant that Nadal needs a new coach if he is to rebound and add to his haul of grand slam titles.
    They echo the thoughts of John McEnroe, although both Stefanki and Bollettieri -- unlike the outspoken seven-time grand slam winner -- wouldn't dispose of the services of Nadal's main coach, his Uncle Toni.
    Nadal, who slipped to 10th in the rankings in June after failing to defend his French Open title, is also helped part time by Francisco Roig.
    "I just think Rafa needs to get a little bit of a different view point," Stefanki told CNN when asked about Nadal, who sports a 2-6 record versus top-10 foes in 2015.
    "Not getting rid of Uncle Toni, either. I don't think that's a good thing. He should probably stay around."
    Such collaborative coaching arrangements have led to success for, among others, top-ranked Novak Djokovic, Roger Federer and U.S. Open finalist Kei Nishikori.
    Stefanki even suggested a name, Andre Agassi. The American, according to Stefanki, employed a smarter brand of tennis late in his career and won five grand slams after his 29th birthday, a feat only matched among men's players in the Open Era by Rod Laver.
    Agassi declined an interview request.
    "I would bring in somebody that knows the type of game that Nadal has to play now to get back," said Bollettieri, Agassi's former mentor, to CNN.
    "Maybe bring in somebody that hears all the gossip on the street, that knows what's going on. But I certainly wouldn't change the foundation."
    Stefanki, a longtime California resident, coached four players who achieved the No. 1 ranking at some stage or another, including Roddick and McEnroe.
    He recalled witnessing a transformation in Nadal's game at Wimbledon in 2008, when the Mallorcan dethroned Federer in what many consider the greatest tennis match of all time.
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    If advising Nadal, one of the first things Stefanki would do is show him a selection of his best performances, the finale at the All England Club seven years ago included.
    "He probably needs to get someone that can say, 'Hey listen, let's go back and watch you play Federer in the final of Wimbledon.' This kid can definitely come back and win another major if he goes back and watches some clips.
    "I coached McEnroe in the twilight of his career and that's what I did. I put together some of the best matches he played, kind of a smorgasbord, and let him watch it.
    "Rafa needs to kind of formulate a view point about the way he wants to go forward with the last quarter of his career."
    Is that something Toni already does with his nephew? It's not known, and CNN's request to speak with the elder Nadal wasn't successful.
    Nadal hinted in May at the Rome Masters that any coaching change was unlikely.
    "If I change someone of my team, it will not be because I'm losing or winning," he told reporters. "It will be that there is not enough motivation from one or another (person.)
    "And remember, my coach is more my uncle than my coach. Family is much more important than tennis."
    Albert Costa, a French Open winner and Nadal's former Davis Cup captain, told CNN that a coaching reshuffle wasn't necessary.
    "He has a very good team," said Costa. "Now he needs time. Time to recover, time to think and time to start to play his best level again.
    "I believe that he is going to achieve it for sure."
    Alejandro Delmas, who has covered Nadal for more than a decade for Spanish sports newspaper AS, said few in Spain are panicking about Nadal's current predicament.
    He did acknowledge that there is some surprise Nadal didn't rebound from his physical problems -- a wrist injury and appendicitis derailed him at the end of 2014 -- the way he has in the past.
    The feeling, he continued, is that a vital victory at a grand slam could reverse fortunes.
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    A "shocked" Stefanki, meanwhile, watched as Nadal exited to the dreadlocked, relentlessly attacking Brown in four sets, puzzled that the twice Wimbledon champion didn't change tactics when serving. Further, he lamented Nadal's "lunging" returns and missing forehand.
    He, like Bollettieri, called for Nadal to strike the ball flatter, something he does in practice, and stand closer to the baseline instead of staying well behind it and reverting to defense.
    "When he beat Federer at Wimbledon, I said, 'Oh my God.' This guy is actually developing a tennis game and isn't just a one-trick pony running every ball down and fitnessing the other guy to death," said Stefanki. "This guy was taking backhands on the rise, hitting winners. He was standing inside the box and ripping winners like Agassi.
    "That's the thing: He can do that. I've seen him do that. He needs to go back to that. And he'll have a lot more fun playing."
    "But if he keeps trying to think he's going to play like a 13-year-old and run around and play defense, it's not going to work. He's not going to win another major."
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    In Hamburg, Nadal topped two players, Fernando Verdasco and Fabio Fognini, who'd beaten him a combined four straight times but he didn't play anyone inside the top 25. Stefanki wouldn't have recommended Nadal showing up in Germany since the U.S. Open is contested on a different surface.
    Overall he would counsel Nadal to enter fewer tournaments. Of the top 10 in the calendar year rankings as of last week, Nadal had played the most events along with Gilles Simon.
    Bollettieri, inducted into the International Tennis Hall of Fame last year, noticed negative body language from Nadal -- which never previously appeared to be an issue -- within the last two months.
    He said Nadal's opponents have lost the "fear factor."
    "What's amazing is that we the fans and coaches can't believe that Rafa is getting beat," said Bollettieri. "It's hard to understand.
    "The biggest difference is that before when there was a long rally, you favored Nadal. That's not so today.
    "The hard-court circuit is going to tell a lot. This summer before the U.S. Open, you're going to get a strong message of whether he can come back or not. Right now he's not the same Rafa. I'm hoping he can come back. He's a great credit to the game."
    Stefanki, too, hoped Nadal would rediscover vintage form.
    "He's got a huge heart, and I just don't want to see him running around backwards," said Stefanki. "That really irritates me. He can't do that at his age. He's got to be a bit smarter."