Michael Phelps has dropped out of one of his scheduled comeback events and will now compete in two races at the US Grand Prix meet in Mesa, Arizona.

The American was originally due to compete in three events as part of the tournament, but has ditched 100 freestyle from his schedule.

"I always have goals and things that I want to achieve and I have things that I want to achieve now," Phelps said. "[Coach] Bob [Bowman] and I can do anything that we put our minds to.

"That's what we've done in the past so I'm looking forward to wherever this road takes me and I guess the journey will start tomorrow."

Phelps, who announced his retirement after the London 2012 Olympics, confirmed plans to return to professional swimming earlier this month.