The buyer of the government's 32.1% share in the wholesale generating company was due to be determined December 17.
A source in UES said the Czech company CEZ and South Korea's Kepco had asked to postpone the sale because they had experienced some technical difficulties, including in obtaining permission to participate from Russia's anti-monopoly service.
The source also said other potential buyers could be NLMK and BasEl.
"I think investment consortiums could be set up for the purchase of the government's package in OGK-4," he said.
Germany's E.ON Russia Power GmbH controls 72.7% of OGK-4.
OGK-4 has a total installed generation capacity of 8,630 MW and incorporates five thermal power plants - one in Western Siberia, one in the Far East, two in central Russia, and one in the Perm Territory in the Urals.
