The British newspaper The Daily Telegraph reported Friday Zardari is expected to recover fully and various Pakistani media reported his condition was stable. He traveled to Dubai for treatment Tuesday.
The Dawn newspaper quoted Zardari spokesman Farhatullah Babar as saying the president's condition was improving but declines to specify the reason for hospitalization.
Babar, quoting Zardari's personal physician, said initial tests "have been within normal range while further tests will be carried out."
Observers speculated Zardari might use his health as a reason to resign. He has been under pressure since the U.S. raid that killed al-Qaida leader Osama bin Laden.
The Telegraph reported Pakistan's interior minister dismissed rumors of a coup.
Separately, the Wall Street Journal, quoting a member of Zardari's ruling party, said Zardari had complained of physical discomfort and was perspiring heavily earlier in the week, prompting his son to urge him to fly to Dubai for a checkup.
The source told the Journal the reason for the Zardari's trip was medical and he had no intention of resigning or seeking asylum. He said Zardari was expected to be in Dubai for about a week.