Underestimate Rafael Nadal at your peril. That is the message from 1971 US Open champion Stan Smith as the world's best prepare to flock to Flushing Meadows.
World number one Novak Djokovic, Roger Federer and Andy Murray headline the US Open, which gets underway on Monday, but two-time champion Nadal is not considered a serious contender compared to years gone by.
Nadal has experienced an up-and-down season on the ATP Tour, with the 14-time grand slam winner 42-14 and 11-6 on hard courts in 2015 after suffering a third-round loss at the Western and Southern Open last week.
One man in his corner, however, is Smith, who believes the 29-year-old Spaniard will come good in New York.
"I think this year at the US Open, the big four are going to be in play. I really believe that Nadal will come back and play well," Smith told Omnisport.
"I don't think he will play poorly although it hasn't been a good year and it may have affected him confidence wise but if you look at the other three they are playing well."
Smith, 68, also singled out 2014 runner-up Kei Nishikori, controversial Australian teenager Nick Kyrgios and big-serving American John Isner as players to watch alongside Federer and Murray.
"Nishikori got to the finals last year and he has been playing well this year," Smith added.
"I know he got hurt at Wimbledon but he is certainly one of those players that's going to be dangerous.
"And you have got some good young players coming up like Kyrgios. You have players like John Isner who nobody wants to play because of his huge serve and he has beaten all of those players.
"You have got to favour the three guys really because Murray really is significant, he has had a great year as well.
"Federer played a terrific match at Wimbledon to beat him but he has won three other tournaments leading up to that and so he is going to be a threat. On the hard-courts he has won it and he knows he can win it again."