"He was a great poet certainly, one of our greatest. And he got the Nobel Prize in 1913 when most of our modern literature was still in the state of formation. His greatness as a poet is there, his greatness as a thinker is there... he wrote plays, he certainly was a pioneer in breaking away from the unexciting commercial plays...he didn't direct great plays. The point is he was a mediocre playwright," said Mr Karnad.
"Rabindranath's plays were not on backward class characters. The Bengali theatre didn't appreciate it... Tagore didn't have the empathy," he added.
His comments drew some angry responses and some critical. Bengali film actor Soumitra Chatterjee said, "It is rather in bad taste. If he were a mediocre playwright, he wouldn't be revered across the world." On Twitter, some tweets mocked Mr Karnad, others were plain angry. "Munnabhai's sage advice to Girish Karnad: Get well soon!" tweeted author and journalist Shobhaa De. Soumik Sen tweeted: "Sad to hear Karnad get over his existential angst at the expense of Tagore. Now he's giving Naipaul more jokes to laugh at."
Last week, Mr Karnad had sharply criticised Mr Naipaul for his views on Muslims in India and had said that the Nobel laureate has no idea of the community's contribution to the country's history.
"Naipaul has no idea of how Muslims contributed to Indian history," Mr Karnad had said during a session on theatre, at the "Literature Live!" literature festival in Mumbai on November 2 where he attacked the Indian-origin writer for his reported visit to the BJP office after the Babri mosque demolition.
Dwelling on Mr Naipaul's anti-Islam stance in his writing, Mr Karnad had said, "Given that music defines our daily existence... you find it in the streets, in the restaurants and so on... you would expect an exploration of India to comment on that... Now Mr Naipaul has written three books on India. If you read them, you find that not even one of them contains any reference to music. He has gone through the whole of India without responding to Indian music. I think that only means that he is tone deaf," Mr Karnad had said.