An aide to Ray, who was also a former Punjab governor and ambassador to the US, said the veteran leader had a kidney ailment and was weak in the knee.
Ray, 89, was taken to the Woodlands Nursing Home in south Kolkata where he underwent a C.T. scan and a series of blood tests.
"The scan has not revealed anything. He is fine. Basically he has been admitted as a precaution," a nursing home spokesperson told IANS. "Two or three doctors have seen him. He is on fluids."Ray was chief minister from 1972 to 1977, the year when the Left Front took power in West Bengal.