The country's prime minister said on Saturday he was in intensive care, after undergoing heart surgery.
A Naftogaz spokesman on Monday denied Dubyna had undergone major surgery but an angioplasty procedure to unclog a blood vessel, adding he was "on the mend" and would soon be able to get up.
A number of Ukrainian politicians have criticized Dubyna after he signed a new gas deal with Russian gas monopoly Gazprom last Monday, finally ending a protracted gas row which led to supplies being cut to some 20 European countries for nearly two weeks.
Tymoshenko said, "The Naftogaz CEO was simply torn in half between two sets of instructions - the prime minister's and the president's. It was complicated for him," adding that despite being offered a low price by Gazprom for Russian gas, Dubyna had been recalled from the talks by Viktor Yushchenko.
On December 31 before last-ditch talks on a new gas deal failed, Gazprom offered Ukraine a gas price of $250 per 1,000 cu m for gas in 2009, about half the current average price paid by Europe. Ukraine, which paid $179.5 last year, refused, however.
In talks last weekend Ukraine agreed to pay a gas price of $450 per 1,000 cubic meters with a 20% discount agreed between Moscow and Kiev for 2009.
