Michael Phelps still can’t bring himself to utter the word “comeback.”

Yet all signs point to the world’s greatest swimmer returning to the pool for the 2016 Rio Olympics.

In the strongest signal yet that his retirement won’t last much longer, Phelps has rejoined the U.S. drug testing program — a necessary step for any athlete hoping to compete in an Olympic sport.

“I have no idea what’s going to happen,” Phelps told The Associated Press on Thursday in an exclusive telephone interview from Minneapolis, where he was attending an Arena Grand Prix meet and even got in some impromptu training in the diving well. “If I really do start getting excited and wanting to do it, I can make that choice. If not, at least it’s something we can say we prepared for.”

Phelps said he’s merely giving himself the option of competing again and stressed that “nothing is set in stone.” But the doping program is a major inconvenience, requiring him to be available for random testing and keep officials apprised of his whereabouts.

“It is a challenging thing to do,” he said. “We are covering all the bases just in case.”

Phelps is the winningest and most decorated athlete in Olympic history. He captured 18 gold medals and 22 medals overall at the last three Summer Games, shattering the previous marks. He is best known for breaking Mark Spitz’s record for a single Olympics by winning eight gold medals at Beijing in 2008.

The U.S. Anti-Doping Agency said Phelps was among the athletes who underwent doping tests in the third quarter, the period ending Sept. 30. He was tested twice.

His longtime coach and close friend, Bob Bowman, said Phelps actually re-entered the doping program near the end of the second quarter, but he wasn’t tested and therefore wasn’t listed in that USADA report. He would be eligible to compete again in March, according to Bowman.

“I just think he’s in a place where he’s feeling good about swimming,” Bowman said. “If he chooses to compete, he’s got some time. I like having the ability to do it. To be perfectly honest, he’s not anywhere near being able to compete in a meet or anything like that. We’re just getting started on improving his fitness. We’ll see where that goes.”

Phelps has been training with Bowman’s team at the North Baltimore Aquatic Club. Each week, he’s working a couple of days in the pool, a couple of days in the weight room, and one or two days on his core training. He has lost about 15 pounds and is back in the low 190s, not far off his competition weight.

“If I decide to keep going and swim again, then I’ll compete,” he said. “If I don’t,” he added, letting out a big laugh, “I guess I’ll re-retire. Just don’t compare me to Brett Favre.”

By subjecting himself to drug testing, the 28-year-old Phelps has given himself plenty of time to go through an entire season before the next major meet, the 2015 world championships in Russia, an important steppingstone to the Rio Games the following summer. FINA, the world governing body for swimming, requires an athlete to be tested for at least nine months before taking part in sanctioned events.

“There’s no grand scheme,” Bowman said. “It just sort of makes sense that he can make some choices if he wants to.”

Phelps attended the world championships in Barcelona this past summer, but he seemed even more pumped about being on hand for one of the more mundane events that fall between the Olympic years.

“Just being around this is exciting for me,” he said from Minneapolis. “It really has been a part of my life ever since I was a kid.”

Phelps’ return would surely be welcomed by the entire sport and even those who only follow swimming during the Olympics.

It was the talk of the deck Thursday.

“I think it would be great for the sport,” said Conor Dwyer, a relay gold medalist at the London Games who trains with Phelps at North Baltimore. “He elevated it so much before that I think it can only get bigger with him in it. Obviously he’s the greatest swimmer of all time — doubled everyone’s medal counts — so to have him on your relay only helps the USA win more golds.”

Phelps’ appeal goes far beyond the pool deck. His recognition factor has often matched athletes from far more prominent sports, such as NBA star LeBron James, a truly impressive accomplishment for a swimmer.

Phelps retired after winning six more medals at last summer’s London Olympics, adamant that all his goals were met and he had no desire to still be swimming in his 30s. He will be 31 by the time of the opening ceremony for the Rio Games — not that old, really, for today’s elite swimmers. One of his top rivals, Ryan Lochte, is a year older and has every intention of competing through the next Olympics.

If there is a comeback, Phelps wouldn’t be doing it for the money, having earned tens of millions of dollars in endorsements during his career. He remains a marketable name, even in retirement, though his endorsement potential certainly goes up if he’s in the water.

More likely, this is another case of an athlete who simply missed the thrill of competition and is still young enough to do something about it, assuming he can find the motivation to endure Bowman’s grueling regimen for nearly three more years.

“There are a lot of things that really excite me … that get me motivated,” Phelps said. “But I swam for 20 years. That’s something that’s going to be very, very hard to top.”