A spokesman for Mikhail Gorbachev says the 82-year-old former Soviet president is in the Kremlin's hospital for tests.
Vladimir Polyakov said Gorbachev was taken to the hospital in suburban Moscow on Tuesday. He said the tests were routine and did not give further details.
Gorbachev complained of health problems at a public lecture in March, and a month later he declined to attend the funeral for former British Prime Minister Margaret Thatcher because of illness.
Since the 1991 collapse of the Soviet Union, Gorbachev has run a foundation for political, social and economic studies.