Dr Singh was questioned on the controversy involving the minister when he was addressing a press conference here after the four day-long Nuclear Security Summit.
"I have heard about these things (allegations against Tharoor). I do not have all the facts before me," the PM said.
"When I go back, I will get all the facts, and in the light of those, if any action is necessary, I think that would be the proper way to proceed. I cannot go by hearsay or what is appearing in the various columns of the newspapers," he added.
The Prime Minister's statement came amid the demands from the Opposition Bharatiya Janata Party seeking the removal of Tharoor over the allegations of corruption and misuse of authority, for helping his close friend Sunanda Pushkar secure an investment in the IPL Kochi team.