IRVINE, United States (AFP) - Olympic superstar Michael Phelps will tackle the toughest test of his comeback this week at the US Swimming Championships, with a return to international competition on the line.
The 29-year-old swimmer's 18 Olympic gold medals include his glittering eight-gold campaign of the 2008 Games - organized with military precision by coach Bob Bowman.
But he's still feeling his way through the comeback he launched in April after a near two-year retirement, not quite sure just how it's going.
"I feel like obviously it could be better," he said. "It could be worse. I think it's been pretty decent, where I've been training and where I am." Mr Bowman said the championships, a qualifying meet for this month's Pan Pacific Championships and for next year's World Championships in Russia, will be the truest gauge to date of how far Phelps has come since he resumed serious training late last year.
"After this week, we'll have a good picture of if he's ahead or behind," Mr Bowman said.
With the start of the 2016 Rio Games precisely two years away from Tuesday, the meeting could offer a starting point for serious discussion of another Olympic campaign by Phelps.
While Phelps has spoken of goals he has yet to accomplish in the sport, he has been coy as to whether he is targeting Rio in his return.
"We just talked about it yesterday," Mr Bowman said. "I think it's a nice little milestone.
"I think we'll see how it goes this week. And maybe if there is anything after that, we'll see how that goes and kind of go from there." Phelps is entered in four events, the 100m freestyle, 100m butterfly, 100m backstroke and 200m individual medley.
In four meets since his return to competition, Phelps has raced four events only once, at the Santa Clara Grand Prix in June.
Coming off of altitude training there, he tied for first in the 100m fly, finished second in the 100m and 200m free and was third in the 200m medley.
"Probably the 100 fly feels the best," Phelps said of the race he has swum the most since April. "Felt pretty good yesterday in the water. Hopefully I can hit a wall and turn and not botch a wall like I have in the past couple races." The 100m free offers the chance to earn a coveted spot on the US 4x100m freestyle relay team - while the 200m medley is an old standby - an event he won at three successive Olympics.
The 100m backstroke is a departure - a challenging event that his old schedule didn't allow for.
"Something we've never done," Phelps said. "Why not try it now? Backstroke always hurts a lot more than any other stroke. It always destroys your legs, but it's interesting.
"It's more exciting for me having a different event and a fun event that I've never really had the opportunity to swim."