The correct answer is - additional stress on the kidney function.
The diabetes if not well controlled can lead to microvascular damage in the early phases, causing such things as diabetic neuropathy or micro-albuminuria.
NSAIDS cause constriction of the afferent blood flow to the kidney. Meaning they constrict the arterial blood flow going to the kidneys. This increases the risk of renal failure. This is seen in diabetes, people with dehydration or patients on ace inhibitors. It can also lead to injury to the kidney if patient receives IV contrast for ct.
Additionally, on rare occasions NSAIDS cause kidney failure to due a rare complication known as interstitial nephritis.