The associate said on Tuesday the diagnosis had been made by the president's two physicians. The associate spoke on condition of anonymity because of the sensitive nature of the information.
A "mini-stroke" is medically known as a transient ischemic attack. It occurs when the blood supply to part of the brain is briefly interrupted, causing symptoms similar to a stroke but not as long-lasting.
Zardari's trip to Dubai last week has led to speculation -- denied by the government -- that he is losing his grip on power.
The associate said Zardari will stay under observation in Dubai for around two weeks before returning home.