As a stereotype, men are often mocked for being big babies when they're sick. When they don't share their sickness, they are also chastised. You can't win.
Not only has our culture often told men that they shouldn't cry, that they're babies when they're sick, we've also been told that we are more manly when we don't show emotions. Now that we're adults, all the rules get changed.
There is also the well-known frequency of denial (which may be part of what we were just talking about), that seems especially the province of men (though we by no means have a full corner on the market).
An additional factor is that some of us didn't have a very respected voice in our family of origin. If that was the case with your loved one, if their were a lot of shut-ups in their childhood, then he will likely continue to shut up. His training has lead him to do so.
Of course, you know and we know that all of this refusal to talk doesn't serve he or you. Of course, counseling can help. But, it may just take some special times where you just sit down together and talk. The reality is that breaking these old familial patterns only happens with practice, with honoring his voice, with mutual respect and with more practice.
Imagine that you're trying to get your husband to get in to see a doctor because he's more lethargic all the time. One approach might be something like this: You sit down alone with your spouse and say, "You know Dear that I love you. I have seen some changes in your health in recent days. You seem more tired and lethargic. I can see that it's not been easy recently. I need you to know that I care and that I'm worried. Please don't tell me not to worry. I need to know that you are taking care of yourself and will take care of yourself. I need you to know that I care. I also really need to know that you're okay. I need you to get a check up very soon (set a date) to see what's going on. We can get through whatever is going on together, if something is going on. I will be with you every step of the way."
Just some ideas regarding this question which I hear often. It frequently goes back to not having been heard in one's family of origin.