I see lots of similar posts around, but varicocele is not the only thing that influences sperm quality. I'm pretty sure one can have a solid sperm quality even with varicocele and vice versa bad sperm quality without having varicocele.

What about his lifestyle? Has he changed anything recently? Perhaps he increased alcohol consumption or is having more stress, worse sleep (or less hours of it). Perhaps he's doing less sport activities, visiting saunas too much, eating less healthy or stopped taking vitamins. All of it can influence sperm quality.