Foreign minister Sushma Swaraj said she was on dialysis at the All India Institute of Medical Sciences, a top government hospital after suffering a kidney failure.
"I am undergoing tests for a kidney transplant. Lord Krishna will bless," Swaraj tweeted.
The 64-year-old BJP leader has been sidelined by poor health on multiple occasions since Modi's Bharatiya Janata Party swept to power in 2014.
There has been no announcement yet that she will formally delegate her duties while she is unwell.