Japanese officials say the former head of Japan's troubled Fukushima-Daiichi nuclear power plant has been diagnosed with cancer, but that it is likely not related to radiation exposure.

A spokesperson at the Tokyo Electric Power Company said Friday that Masao Yoshida has informed the company that he has cancer of the esophagus.

The 56-year-old Yoshida stepped down last week after being hospitalized for an unspecified illness.

Japanese media have speculated that Yoshida's health problems were related to his efforts to stabilize the nuclear facility.

TEPCO officials say Yoshida's radiation exposure did not exceed the recommended limit for emergency workers.

Many Japanese consider Yoshida a hero for defying orders not to flood the crippled Fukushima-1 reactors with seawater, thus preventing what could have been a much larger radiation disaster.

The plant director was also one of the first TEPCO managers to offer what was seen as a sincere apology for the crisis.

Yoshida had pledged that the crippled reactors would be brought to a stable condition of cold shutdown by the end of this year.

The Fukushima power plant was crippled by March 11 by a massive earthquake and tsunami. A series of subsequent explosions triggered by reactor meltdowns spread contaminants over a vast area of the country.

Though no deaths have been directly attributed to the crisis, tens of thousands of people were forced to flee their homes due to leaking radiation.