The court cannot afford to replace "a significant number of key international legal and other staff", judges said, in the latest setback to a trial stalked by fears that its octogenarian defendants will not live to see a verdict.
"While there is insufficient staff to support the work of the trial chamber, it cannot continue to sit for four days each week," presiding judge Nil Nonn said in court, adding that hearings would be three times a week from next month.
"This will lead inevitably to an extension of the time needed to conclude the case," he said.
The move comes as the oldest and most frail of the accused, ex-Foreign Minister Leng Sary, 86, is in hospital with a string of ailments, lending fresh urgency to proceedings that have already been hit by health-related delays.
The tribunal, which is funded by foreign donors, has faced frequent cash shortages since it was set up in 2006 to seek justice for up to two million people who died under the 1975-1979 Khmer Rouge regime.
It has spent over $160 million so far and faces a shortfall of at least $4 million this year.
Observers blame the donor fatigue in part on stubborn allegations of political interference at the court and complaints it is moving too slowly.
Co-accused Ieng Sary, "Brother Number Two" Nuon Chea and ex-head of state Khieu Samphan deny charges including war crimes and genocide.
To speed up their complex case, it was split into a series of smaller trials, starting with the forced evacuation of the population into labour camps and related crimes against humanity.
But given the age of the accused and the funding crisis, tribunal monitors believe this first "mini-trial" will also be the last and the trio will likely never have to answer for the worst atrocities.
Led by Pol Pot, who died in 1998, the Khmer Rouge wiped out nearly a quarter of the population through starvation, overwork or execution in a bid to create a communist utopia.
The court has completed just one case, sentencing former prison chief Duch to life in jail for overseeing the deaths of some 15,000 people.