Dr Ling Liong Sik has an axe to grind with Prime Minister Najib Abdul Razak, according to former MCA president Dr Chua Soi Lek.

Hence, Chua told Malaysiakini , he could understand the reason behind Ling calling on the prime minister to relinquish his post.

"As a veteran politician, Ling is entitled to his opinion. I can understand where he is coming from. He feels sore after being charged," he said.

Chua was referring to the Port Klang Free Zone (PKFZ) case.

Ling, who was a former transport minister, was charged in 2010 - a year after Najib became prime minister - on three counts of cheating the government. He was acquitted in 2013.

Meanwhile, Chua said it could not be denied that Mahathir's testimony in the case had helped Ling to secure an acquittal.

"Furthermore, given the long association between Ling and Mahathir, he (Ling) is more indebted to Mahathir than Najib.

"And with Mahathir committed to removing Najib, Ling is attempting to help him," he added.

However, Chua said he agreed with certain Umno leaders that his predecessor' remarks would further strengthen Najib' position .

"By convention, the prime minister represents all Malaysians, but by tradition, the PM comes from the dominant party, which is Umno.

"Umno does not like outsiders to interfere in its internal affairs. So what Ling said will help Najib (to consolidate his position)," he added.

During an event over the weekend, Ling said he agreed with Mahathir 's call for Najib to step down because "he has taken people's money and put it in his own personal accounts".

Najib is embroiled in controversy over the deposit of RM2.6 billion into his personal bank accounts.

The prime minister has denied taking public funds for "personal gain" while his supporters claim the massive deposits were "political donations" from the Middle East.

Najib has since issued a legal letter to Ling, warning him of legal action if he does not apologise for his statement within seven days.