However, USA Swimming executive director Chuck Wielgus told ESPN.com that Phelps may yet be allowed to participate at the meet in Russia.
"It's complicated, but there are ways in which it could happen," Wielgus said. "There's a pathway for things to be reconsidered... or considered."
Phelps has yet to comment publicly on whether or not he might swim in Russia but is expected to make his comeback at a U.S. Grand Prix meet in Arizona next month.
The 29-year-old has already qualified for the American world championships team in three individual events: 100 metres freestyle, 100m butterfly and 200m medley. He could also expect to be selected for three relays.
Phelps announced he was quitting the sport following the 2012 London Olympics after he signed off with a record tally of 18 gold medals dating back to Athens 2004.
However, he had a change of heart last year and decided to get back in the pool and set his sights on the 2016 Rio Olympics.
This year's world championships were supposed to form a major part of his preparations but his plans were ruined when he was charged with a drink driving offence in December.
Phelps was given a one-year suspended prison term and sentenced to 18-months of supervised probation. He was also banned from drinking alcohol and ordered to attend an addiction treatment centre.
He apologised for drink driving and promised to make amends. Last month, he announced his engagement to Nicole Johnson, a former Miss California USA.
USA Swimming did not make any official comments on whether Phelps could be cleared to swim in Kazan but one of his long-time team mates, Natalie Coughlin, told ESPN he had served a long enough penalty.
"Not only do world championships fall outside the six-month suspension but it also punishes his team mates, particularly those that would share a relay spot with him," Coughlin wrote in a text message to ESPN.
"We always want to have the best people racing and he has proven himself to be the best, time after time."
(Reporting by Julian Linden in Singapore; Editing by John O'Brien)
Share
