The Russian airline Aeroflot has apologised to passengers on a transatlantic flight after one of its pilots made such a slurred preflight announcement it created panic on the plane that he was drunk.

The garbled message from one of the plane's two captains, Alexander Cheplevsky, prompted a passenger revolt that forced the airline to replace all three pilots on the Boeing 767 before it took off from Moscow to New York on 28 December last year.

Aeroflot today denied the 55-year-old had been drinking, but they accepted he was in a poor physical state and said sorry to those on board.

Lev Koshlyakov, deputy director general of Aeroflot told the Guardian: "We accept that his physical condition was not good. We acknowledge the mistake and apologise to passengers."

Koshlyakov confirmed that Cheplevsky had celebrated his birthday the day before the incident, but said no trace of alcohol had been found in his body after a series of tests. Aeroflot claimed the pilot may have suffered a stroke before making his incoherent preflight announcement to passengers.

"The first thought that occurred to me was, 'this guy is drunk'," one passenger, Khatuna Kobiashvili, told the Moscow Times. "His speech was so slurred it was hard to tell what language he was speaking."

When passengers, including the Russian TV presenter Ksenia Sobchak, began to ­protest, they were told to "stop making trouble", according to the paper, whose reporter was also on board. But the crew could not calm the panic, and after an hour of angry exchanges the pilots were replaced.

Koshlyakov said: "A couple of passengers started very aggressively crying out that the pilot was drunk. In those circumstances passengers are easily subject to panic, and the crew was not able to pacify them." But he added: "I understand their concerns, the situation could have been dealt with differently."

Cheplevsky is being treated in hospital. "As soon as he is fit he will be interviewed as part of our internal investigation," Koshlyakov said. He added: "We have interrogated the crew members who said his condition deteriorated. If he was unfit to fly that was very irresponsible. Hypothetically the other pilots would have controlled the situation, but this is not an excuse."

Koshlyakov said it was unlikely that Cheplevsky would be allowed to fly again.