INDIANAPOLIS — Michael Phelps has withdrawn from the 100-meter freestyle at the U.S. national championships because of a sore neck.

The superstar swimmer was supposed to swim in the last heat Friday morning, but he was still in pain after waking up a day earlier with a kink in his neck.

Phelps says he swam through the pain in setting a world record in the 100 butterfly Thursday night. The 100 free was going to be his final event at nationals.

He has qualified for the world championships later this month in the 100 and 200 flys and the 200 free. It's likely Phelps will swim on three relays in Rome.

Even if he had qualified in the 100 free, Phelps says he wouldn't have swam the event at worlds. The swimming events begin July 26.