
A lot will depend on wher in the abdomen the missing teste is. My friend had a dog to show and he had only oje, and she wanted to know if it would come down before he got too settled with her.
If it is above the Inguinal ring then it will not be able to come down, as it will be too large to pass sown this late, but if it is below this it still has a chance.
She went to a vet who was an expert with Ultrasound, prinmarily using it as a diagnostic tool with Cancer etc. He was able to find the testicle and confirm that it was in fact above the Inguinal ring, and the pup was able to be rehomed in a pet home at 5 months. He is now about 18 months or two years and still unilateral, and will be castrated.