"The maestro is in Moscow, in the hospital," the family friend said, without specifying when the cellist went in.
The world famous virtuoso spent a few months in a Moscow clinic after he felt unwell during his December tour to Vononezh, southern Russia.
Some Russian media said Rostropovich had undergone treatment at an oncology center in February, where his liver was operated on following a course of therapy in Switzerland and France.
The husband of renowned opera singer Galina Vishnevskaya - a musical union which has lasted more than 50 years - Rostropovich was repeatedly decorated for his achievements in Soviet times, but had his Soviet passport withdrawn in 1978 for criticizing the government's excessive interference in art and culture. In 1974, he left the country for the United States, where he lived with his family until his citizenship was restored in 1994.
The Times newspaper has called him the greatest of contemporary musicians. Rostropovich's name is on the list of 40 honorary members of the Academy of Arts in France, and he is the head of the organizing committee of the 13th International Tchaikovsky Competition.
