Andy Roddick says he wonders sometimes if he retired too soon seven years ago at age 30. After all, he’s seen the “Big 3’’ continue their excellence well into their 30s.

But then Roddick returns to reality. He realizes the members of this trio — Roger Federer, Novak Djokovic, Rafael Nadal — are superhuman, even unappreciated as far as their place in history.

“I had some left in the tank,’’ Roddick told The Post on Thursday at a promotional event. “But these guys are dominant. If anything, they’ve gotten better over the last seven years since I retired. You always wonder. But I’m really happy with what I’ve done since retirement. I don’t have any regrets.

“I’m certainly happy to be a fan and watch these guys march to the record books. It’s an amazing time. I hope people are appreciating what they’re seeing.’’

Again, the U.S. Open is the Big 3 versus the rest of the field when the tournament kicks off Monday. Djokovic, Nadal and Federer are the top three seeds — led by defending champion Djokovic.

The tennis world still awaits for “The NextGen’’ — as the ATP website brands the group of younger contenders — to rise in a meaningful way.

“It’s not just dominant for their generation,’’ Roddick said. “They’ve almost taken away another generation of potential slam winners. You’re talking about the three best of all time — the racket skills of Roger, the discipline of Novak, the physicality of Rafa. They don’t have to prove anything else, yet they still prove it time after time.

“I remember Roger was carrying a back injury into the U.S. Open in 2013. People were talking after he lost to Tommy Robredo, whom he hadn’t lost to before: Is this the end? And here we are six years later, he’s one shot from winning Wimbledon and still winning majors.’’

Still, Roddick thinks Djokovic and Nadal have a stronger chance than the 38-year-old Federer does at this year’s Open.

The draw was staged Thursday, and the drama in the men’s draw concerned which half of the draw would feature two of the three. None of the three greats wants to have to beat two of his rivals to win it all.

Djokovic and Federer drew the short straw. They could meet again in the semifinals and resume their rivalry that peaked in the Wimbledon final in July. Djokovic saved two match points to win an epic marathon — 13-12 in the fifth set.

Roddick believes Federer may still feel the toll as he has suffered through a rough go in the Open tune-ups.

“The two clear favorites are Novak and Rafa,’’ Roddick said. “Roger is low on match-practice. And that loss was tough at Wimbledon. He’s going to need the crowd and be lifted. Fortunately, I’ve never seen a guy more beloved than Roger. He’s going to be searching for form because he doesn’t have a lot of matches. If he can get through the first week clean, he’ll have a shot.”

Djokovic faces a rough draw even before Federer. Dangerous American Sam Querrey looms in Round 2 as does a quarterfinal against summer sensation and No. 5 seed Daniil Medvedev of Russia. Medvedev beat Djokovic in the last Open tune-up in Cincinnati on the way to the title.

“I think most of the players study the draw, to be honest,’’ said Djokovic, who attended the draw ceremony. “Even if they say, ‘Well, I’m just looking at my next match’, but you still look at your section and who is in there and … you scout. You have your team of spies overviewing all the courts and potential opponents.’’

If Djokovic survives, it would be his 17th Grand Slam title — three behind Federer’s record. Can he catch the Swiss Maestro? Nadal, 33, sits in second with 18 Grand Slams.

“It’s trying to choose the Oscar winner without seeing the last 25 percent of the movie,’’ Roddick said when asked if Djokovic can set the record. “You’re asking me to predict health. I put it even-money across the board for all three of them to finish with the record.

“Novak is the most dominant day in, day out. Rafa has put his flag on the ground at the French and Roger is still able to win Slams. It is remarkable.’’

What isn’t remarkable is the plight of American men’s tennis since Roddick bid the game adieu. The man who once served at 153 mph at the Open is the last American to win a Grand Slam men’s title, in 2003. Reilly Opelka, a 6-foot-11 up-and-comer; Taylor Fritz, now ranked 27th; and Frances Tiafoe are the latest three hopefuls.

“The raw potential is there,’’ Roddick said. “Frances is super athletic, you can’t teach 6-11 with Reilly, and Fritz’s shots cut through the court. You see the tennis skills. They’re all top-20, top-10 prospects. But you have to see how they operate: Are they putting the right thing in their body? Will they treat this like a profession or hobby? I do think there’s a group of them and we’re not pointing a finger at just one of them with that burden.’’