The Iberian lynx, found only in Spain and Portugal, could become the first big cat since the sabre-toothed tiger to die out, a WWF report claims.
Road deaths are now the greatest cause of mortality for the lynx
The critically endangered animal could become extinct within five years unless swift action is taken, the group says.
Lynx numbers have declined from 100,000 at the beginning of the 20th Century to around just 100-120 today.
Dam building, road deaths, hunting and a decline in wild rabbits have led to the cat's downfall, the report says.
The EU and the government of Spain have actively contributed to the Iberian lynx's decline, WWF claims, by building a road through one of its last remaining habitats.
"It is ridiculous that the European Commission is supporting projects aimed at protecting the Iberian lynx on the one hand, while funding road and dam schemes that are pushing it to extinction on the other," said Callum Rankine, of the WWF.
Accidental deaths caused by speeding vehicles on Spain's expanding road network are now the greatest cause of mortality for the lynx.
Just two years ago, there were thought to be 160 individuals, five years ago there were 400; so the species is in a nose-dive, WWF has said.
According to a recent study carried out by WWF and the conservation organisation SOS Lynx, there are only about 21-25 breeding females in two isolated populations in southern Spain.
The WWF has been urging the Spanish authorities for over two years to close the Villamanrique-El Rocio road, which crosses the heart of Doņana Natural Park and fragments of critical lynx habitat.
The road was part-funded by the EU, and several lynx have already been killed on it, WWF claims.
"Unless something drastic happens rapidly, the Iberian lynx is a dead cat walking," said Mr Rankine. "With such a small population, the accidental loss of just one individual on the road brings the species closer to the brink of extinction."
The WWF is also calling for lynx habitat to be covered by the EU's Natura 2000 Programme, which offers the strongest level of protection in Europe.
Currently, the areas proposed by Spain for Natura 2000 designation do not cover the biological corridor that could be used to connect the remaining breeding population in Doņana National Park with the one in Sierra Morena.
"These two populations are the last hope for the survival of the species," said Mr Rankine. "The EU must take species conservation seriously."