Michael Phelps' comeback took a major hit on Monday, with USA Swimming suspending the 18-time Olympic champion for six months and forcing him to withdraw from next year's world championships.

Phelps also lost six months of funding from the sport's national governing body as a result of his second DUI arrest. The 29-year-old swimmer is banned from participating in USA Swimming-sanctioned meets through April 6, 2015.

USA Swimming said Phelps violated its Code of Conduct and cited a section of its 2014 Rule Book in punishing him. Its executive committee approved the sanctions, which take effect immediately.