Defence Minister Mohamad Sabu says that former premier Najib Abdul Razak is "not a gentleman" for criticising him outside the Dewan Rakyat.

"I don't want to respond to comments made outside, I want to answer in the Parliament. Commenting outside is like hitting below the belt.

"Not gentlemanly, come comment in here (the Dewan Rakyat)," he told reporters at the Parliament lobby today.

Mohamad, the Amanah president, was responding to a jibe made by Najib at BN campaign event in Sungai Kandis last night.

Najib said that he had no confidence in Mohamad's ability to head the Defence Ministry, describing him as mere comic relief.

"Our defence minister is a cartoon. He wears the beret like a cartoon (character). He gets into a warship and talks about fish curry.

"You are the defence minister. Talk about the country's defence policies, not about fish curry.

"This is not defence minister material. This is a joker," the former BN chairperson was reported saying by news portal Free Malaysia Today.

The fish curry was in reference to Mohamad's academic background in food sciences, and his penchant for cooking, even after he assumed his ministerial post.

Najib had twice served as the defence minister, for a total of 14 years.

Mohamad also said that it was too early to make any judgement about his performance as defence minister.

"I've only been a minister for two months. How to assess someone in two months? The time has not come.

"My focus is on the defence ministry, when I'm finished serving there, then the judgment can be made," he said.