Laszlo Cseh (HUN), the triple Olympic silver medallist of 2008, has been rushed to hospital on arrival in Rome. The European medley and butterfly record holder is suffering from a stomach virus.
A source close to the Hungarian team told SwimNews: "He has had to have rehydration and electrolyte drinks but is quite sick."
Cseh's 13th world-championship campaign was due to have started with the 200m butterfly at the Foro Italico on Tuesday. He was expected to rejoin battle with Michael Phelps after taking silver behind the American in Beijing last summer.