Two lurchers have been found in a similar poor state at separate times in Brighton and Hove within a week.
An animal welfare officer said that they had identical conditions – dehydrated with a high temperature – although it was not yet known how they became ill.
The first to be found was a young male brindle lurcher, believed to be about four months old.
The dog was spotted on grassland at the side of the Asda superstore in Crowhurst Road, Hollingbury, last Thursday (26 July) by a member of the public.
A vet put the dog on a drip over the weekend and although it was unclear whether he would survive he has since begun to get better.
A second lurcher was found on Monday (30 July) near the West Hove Sainsbury’s store in Benfield Valley by a young boy.
The outlook for the fawn rough-coated lurcher is uncertain although the dog, believed to be two to three years old, was also put on a drip.
Brighton and Hove City Council animal welfare officer Sue Watson said: “There’s an air of mystery surrounding these two dogs.
“We don’t know if there are any more lurchers in the city that are suffering from the same illness and we don’t know how these dogs became unwell.
“It’s possible that the recent hot weather might be responsible. It’s vital that pets are kept cool and are provided with enough fresh water.”