If a testicle atrophies a fair amount from an infection but is treated and didn't lose all it's mass can it still produce testosterone just less?

Testosterone: Since most of testosterone is produced in men in the testicles In males it is possible that yours may be low, but the only way to know is to check levels. Signs of low testosterone may create early or late puberty, Infertility, erectile dysfunction, low level of sexual interest, infertility, and thinning of the bones.

Yes: The best way to tell how much it's producing is to have blood work for testosterone levels drawn. See your doctor to have this done.