Union Finance Minister Pranab Mukherjee and West Bengal Chief Minister Buddhadeb Bhattacharjee also accompanied Singh and spent some time inquiring about Basu's health.
Basu's health condition deteriorated on Wednesday morning, Jan 6, following which he has been put on a ventilator for the last 24 hours.
There are reports that despite Basu's condition critical, his blood pressure has stabilized.
Basu is being treated for pneumonia at the AMRI hospital in Salt Lake here.
The veteran leader was admitted here on Friday, Jan 1, following a severe chest infection.
The doctors after conducting a proper check-up had earlier detected that he was suffering from slight pneumonia.