Rahul told the media here that he wanted to personally wish the DMK Chief a speedy recovery.
On Thursday night, the former chief minister was admitted to the hospital for the second time in the last three weeks.
He was first admitted to the same hospital on December 1 for optimisation of nutrition and hydration and was discharged after he improved substantially
The hospital issued a statement saying Karunanidhi was readmitted with breathing difficulty due to throat and lung infection, adding that he was stable and being treated.
Karunanidhi's daughter and Rajya Sabha MP from Tamil Nadu Kanimozhi said that he had some lung infection and breathing difficulty, adding that he was much better now.