Translation:He is going to suffer because of his illness.
"suffer from" translates to "sufrir de". When you see "por" come after verbs like this it means because of.
"suffer from" is an incorrect translation for "sufrir" because then you would get an awkward translation: He is going to suffer from because of his illness. When you have "por" directly following you don't need extra prepositions..
I can see what you mean though however it's not what this example is saying. Your sentence would be "ël va a sufrir de su enfermedad". he is going to suffer from his illness. Hope this helps!
It is hard to detect a difference in English between "suffer from his Illness" and "suffer because of his illness." On the other hand I think "suffer for" suggests that the result is self-inflicted. You can suffer from sunburn, you don't suffer for sunburn -- but you can suffer for your decision to lie in the sun. Am I right?
One correct solution reads: "He is going to suffer for its illness." It's hard to see what this could mean. Again, "He is going to suffer for his illness" could mean something, but not what the Spanish sentence means. It would mean something like someone else is going to make him suffer because of his illness.
To reinforce what others have written, there is no difference in English between: "He is going to suffer from his illness." and "He is going to suffer because of his illness." The first one sounds far more natural, and I think it should be counted as correct.