Caeleb Dressel knows the age-group days of "simply swimming" can never return for a seven-time Olympic gold medalist.

But despite devastating lows that drove him away from the sport for the better part of a year, and his admitted uncertainty over whether he'll ever return to his best, the 27-year-old American once touted as the heir to Michael Phelps is ready to test himself again at the Paris Olympics.

"I don't know what's possible," Dressel said after a rollercoaster U.S. trials, where he won the 50-meter free and 100 butterfly to earn a chance to defend two of his three individual titles from the pandemic-delayed Tokyo Games.