Solana said Serbia should use the time to convene parliament and renew the mandate of its Kosovo negotiating team.
Belgrade has said that without a renewed mandate, no officials could legitimately represent Serbia in the Vienna talks.
"I don't think we should risk credibility for a question of a week," Solana said. "We want them to get engaged and move the proposal ahead."
Martti Ahtisaari, the UN Kosovo mediator, unveiled a plan last Friday which sets Kosovo, whose population is 90 per cent ethnic Albanian, on the path to independence.
Nato wrested control of the province from Serbia in 1999 to halt slaughter and ethnic cleansing of the Kosovans at the hands of the Serbs.
Serbia opposes independence, offering the Kosovo Albanians "substantial autonomy", which they reject.
The six-power Contact Group on Kosovo already postponed Ahtisaari's plan once last November in order to avoid inflaming nationalist passions in the Serbian general election on January 21.
Diplomats say that patience is running out among Kosovo Albanians, who blame the eight-year political limbo for the stagnant economy and 50 per cent unemployment.
They say that lengthy delays could spark further unrest in the province, swept in 2004 by riots against the Serb minority. Kosovo Albanian political activists have called a protest for Saturday, saying Ahtisaari's plan falls short of independence.
Solana echoed this concern over possible violence, saying he hoped that the Kosovo institutions and people will be "up to the responsibility of this time".