Could you please be more specific formulating your question. Decrease levels of testosterone will ultimately be associated to testicular atrophy and changes will depende on the length and degree of the injury and the cause of the decrease in testosterone. Is it due to testicular injury?, what is the cause?, is the hypothalamic - pituitary axis etc.. You are looking at human pathology or experimental induced in animal models etc.
I agree with Olga above. - l might also expect some changes related to volume of sperm production. Primarily with in that dangerous tubular but also ? Within the interstitial Leydigs. Especially over extended period.