"It is a case of multi-organ failure. Three organs- lung, kidney and the haemo dynamic system - have failed and his heart is partially affected. His condition sank earlier, then stabilised. He is sinking again now," Dr Susruth Banerjee, a doctor on the medical board of AMRI Hospital.
Basu is now totally dependent on life support, he added.
There has been reportedly a sharp fall in his blood pressure.
"His kidney is dependent on dialysis, lung on ventilation and haemo dynamic system on medicine," Dr Banerjee said.
Continuing with the dialysis which began on Thursday, Jan 14, Basu underwent three-hour dialysis on Friday, Jan 15.
The former West Bengal chief minister would undergo another dialysis on Saturday, Jan 16.
Basu was hospitalized with pneumonia on Jan 1 and has been put on ventilator support since Jan 6.