"Because they have defamed (my family), I have to sue them or demand they retract what they said in Harakah," Najib told reporters here Friday.
"What was reported in Harakah was defamatory and completely untrue. They did not show evidence. So it is my right to defend myself and my family," he added.
He refused to comment further on the matter.
It was reported on Thursday that Najib had instructed law firm Hafarizam Wan & Aisha Mubarak to hand over a letter of demand to Harakahdaily managing director Dr Rosli Yaakop to retract the article and publish an unconditional apology in writing.
The article was a commentary piece based on a New York Times article earlier this month.
Najib was speaking reporters here after launching the start of Sri Aman Minor Specialist Hospital's construction.
The RM150mil 108-bed hospital, first announced in 2011, is targeted for completion in 2018.