Three rare black foxes escaped in a suspected break-in at a temporary enclosure in Essex.
The animals, which had come from a farm in Wales, went missing from a garden in Mile End, Colchester on Thursday night.
Richard Aston, who has looked after the cubs since their rescue, said the female had been found but he feared for the safety of the two males.
He said social media posts said local hunts may be preparing to track them.
The animals are a type of North American red fox with a trait that makes their fur silvery-black.
They were being kept overnight at Mr Aston's parents' home where a hole was found at the back of their outdoor enclosure.
Mr Aston, a 33-year-old rare animal expert, said people should not approach the foxes which were captive-bred and he was "extremely concerned" for their welfare.
"They have a couple of medical conditions, one loses all his fur during breeding season and they need certain dietary requirements," he said.
"They're also not road savvy at all, they have no fear of it whatsoever."
Black Foxes UK said: "Around 0.1% of foxes in the UK are melanistic (black) by our records. These escaped foxes are not a native species.
"The UK remains a world centre for the trade of 15 million fox pelts a year, despite a ban."
Mr Aston added he had contacted Essex Police and the RSPCA about the foxes.
Correction 1 May 2019: This article has been amended to clarify that the animals originally came from a farm in Wales.