"We are now sure that we can confirm which substance caused this illness," Dr Nikolai Korpan, who supervised Yushchenko's treatment at Vienna's Rudolfinerhaus clinic, was quoted as saying in Wednesday's edition of the newspaper.
"He received this substance from other people who had a specific aim," he added. Asked if the aim had been to kill Yushchenko, Korpan said: "Yes, of course."
Yushchenko fell ill in September while campaigning for Ukraine's Oct. 31 presidential polls. He later accused the authorities of trying to kill him with some kind of chemical poison.
His previously smooth face has become pocked with cysts and lesions.
Korpan said the substance could have been administered via food, water or an injection.
"We need to check him again here in Vienna," said Korpan. "If we received him today, we could finish the whole investigation in two or three days."
One theory was that Yushchenko was poisoned with dioxin, which causes a severe form of acne called chloracne, but Yushchenko was never tested for that.
The election, which produced a winning vote for Moscow-backed Prime Minister Viktor Yanukovich, triggered mass protests. It was later annulled by the Supreme Court and a December 26 date set for a rerun.
Efforts to resolve deadlock over electoral reform have stalled, and led to friction between the West and Russia, which blocked U.S. and European diplomatic efforts to ensure a re-run.