Brazil's population of the scaly-backed animal has shrunk by more than a third over the past decade as the area covered by the dry shrubland where it lives has halved, the IUCN said on the eve of the tournament's kick off.
The Brazilian armadillo -- which provided the inspiration for World Cup symbol Fuleco -- was named by the International Union for the Conservation of Nature as one of many species under threat worldwide.
The IUCN, which works closely with governments, the United Nations and other environmental groups, also warned that 94 percent of wide-eyed primate lemurs are threatened with extinction.
Of the 101 surviving species, 22 are under threat -- including the biggest, the Large-bodied Indri, and the smallest, Madame Berthe's Mouse Lemur -- the nature group headquartered in Gland in the canton of Vaud said.
Lemurs are threatened by destruction of their tropical forest habitat in Madagascar.
Political uncertainty and rising poverty have accelerated illegal logging, the IUCN explained, adding that hunting of the animals for food had also emerged as a serious issue.
Orchids on the edge
In the plant world, the group warned that close to 80 percent of temperate Slipper Orchids now face extinction.
The finding was based on a global assessment of the species, which is easily recognizable thanks to its slipper-shaped flowers, which trap insects to ensure pollination.
It is found in North America, Europe and temperate regions of Asia.
The IUCN blamed habitat destruction and excessive harvesting of wild species for sale.
"What was most surprising about this assessment was the degree of threat to these orchids," said Hassan Rankou of the IUCN's orchid team, which is based in the Royal Botanic Gardens in London.
"Slipper Orchids are popular in the multimillion-dollar horticultural industry," he said.
"Although the industry is sustained by cultivated stock, conservation of wild species is vital for its future."
Among the most at-risk species are the Freckled Cypripedium, with less than 100 left in Yunnan in China and the Ha Giang province of Vietnam.
Also under threat are the national flower of the Cayman Islands, the Banana Orchid.
Turning to the globe's rivers and oceans, the IUCN said that the Japanese Eel -- a traditional delicacy in Japan and the country's most expensive food fish -- was also in danger.
It had been hit by habitat loss, overfishing, barriers to migration, pollution and changes to oceanic currents. Its decline has driven a rise in trade in species such as the Shortfin Eel, the IUCN said.
Still, there was also good news.
The IUCN said it had raised its rating the Yarkon Bream, a fish found only in Israel, from extinct in the wild to vulnerable.
Its habitat was wrecked by drought and drawing water for irrigation, but it was saved by taking 120 of the last wild fish into a captive breeding programme at Tel Aviv University.
Its population has increased significantly since 9,000 laboratory-born Yarkon Bream were released into restored habitats in the Yarkon and other Israeli rivers, the IUCN said.