Mahathir, whose enmity with Prime Minister Abdullah Ahmad Badawi surfaced last year, said in an interview published Wednesday that Abdullah's deputy, Najib Razak, was "the better candidate."
Mahathir told independent news Web site Malaysiakini.com that before he retired in 2003 after 22 years in power, he had considered handing the office to Najib instead of Abdullah.
"If it is a comparison between (Abdullah) and Najib, I would say that (Abdullah) was less qualified," he said. "But I also thought that he (Najib) was, maybe, a little bit young, so he should give an older person a chance. That was why I decided on Abdullah."
Asked whether he believed Najib, 53, is still the best person to lead Malaysia, Mahathir said, "I think if Najib is not so afraid of losing his (current) position if he displeases the prime minister, he would make a good prime minister."
Mahathir's comments appeared to be aimed at driving a wedge between the 67-year-old Abdullah and Najib, both of whom have repeatedly voiced confidence in each other and denied speculation of any friction. Malaysia's Cabinet and ruling party leaders have also said they support Abdullah completely.
Mahathir's main aide did not immediately answer calls on his mobile phone. Abdullah's aides could not be reached for comment.
Mahathir began attacking Abdullah for alleged nepotism and weak governance in mid-2006, but the 71-year-old elder statesman has largely steered clear of open criticism following a mild heart attack in November.
Mahathir has not presented proof to back up his allegations, and Abdullah has refrained from retaliating against Mahathir while vehemently denying the accusations.
In his interview with Malaysiakini, Mahathir said he believed Najib, who has also served in recent years as defense minister, would not have aborted Mahathir's vision of building a new bridge to neighboring Singapore.
"I think our world views will be slightly different, but by and large, they are more or less the same," Mahathir said. "I wouldn't say, for example, that Najib would drop the bridge. He was talking about building the bridge to the very last moment."
Najib was on a visit to the United States, and his aides could not be reached for comment.
Abdullah announced the scrapping of the bridge project last year, saying Malaysians were unhappy with Singapore's preconditions for the plan. Mahathir has accused Abdullah of compromising national interests and being too afraid to negotiate properly with Singapore.