Japan Post Holdings Co. President Taizo Nishimuro is set to step down for health reasons, with the head of the postal group's banking unit likely to succeed him, sources said Saturday.

Nishimuro, 80, has been hospitalized since last month where he has undergone unspecified tests.

The government, still the biggest stakeholder in the group even after last year's mammoth public offerings for the postal, bank and insurance arms, is now planning to pick Japan Post Bank President Masatsugu Nagato to succeed Nishimuro as early as April, the sources said.

Nagato, 67, former chairman of Citibank Japan, assumed his post last year. He joined what is currently Mizuho Bank in 1972 before moving to Fuji Heavy Industries Ltd., where he rose to vice president.

Nishimuro became president of Japan Post in 2013 after heading Toshiba Corp. and the Tokyo Stock Exchange, managing the huge stock listings last November of Japan Post as well as Japan Post Bank and Japan Post Insurance Co.

Like other financial institutions, however, the group has been facing difficulties managing its assets given lower interest rates following the introduction of the Bank of Japan's negative rate policy earlier this year.