Akhmed Zakayev on Thursday strongly endorsed Sadulayev and dismissed concerns that his appointment could undermine international support for the separatist movement.
"I know this person very well," Zakayev said. "It is a new name and therefore there are all kinds of rumours and supposition. But I warrant to you, as people deal with him directly as head of state, it will become clear. Everything will fall into place. He is not an extremist. He is not a fundamentalist."
Russian officials say Maskhadov was killed in a special forces operation in a Chechen village last week.
Sadulayev, whom some analysts have identified as a radical Muslim, has emerged as Maskhadov's likely successor.
His probable succession has prompted speculation and some say that Sadulayev would be a figurehead while real power is wielded by Shamil Basayev - the commander who claimed responsibility for the Beslan school-hostage last September, which ended in the deaths of some 330 victims.
Maskhadov was killed last week
by Russian special forces
When asked who Maskhadov's successor was, Zakayev said Sadulayev. Asked if Basayev was a successor, he responded: "No."
Maskhadov led the separatist forces in Chechnya that fought the Russian army to a standstill in 1996, then was elected president of the republic when the Russians withdrew.
Regarded as a comparative moderate and secularist among the separatists, he retained respect in some Western circles.
But Moscow staunchly rejected Maskhadov's calls to negotiate a peaceful end to the conflict. The Kremlin said he was involved in terrorist attacks such as the Beslan school raid and the seizure of a Moscow theatre in 2002, in which 129 people were killed.
Maskhadov had denied any involvement in either attack.
Zakayev insisted that Maskhadov's commitment to peace would be echoed by Sadulayev.
Zakayev said Maskhadov's young
successor seeks a Chechen peace
"The course that president Maskhadov started, both in terms of domestic and foreign policy, will be taken up by those that follow him because there is a legal basis for the resistance and for the structure of the Chechen state," he said.
"I give you my absolute word that the objective of those who succeed Maskhadov is to find a peaceful solution to this conflict."
Russia alleges that Zakayev was a senior Chechen military commander who fought against its troops in the late 1990s.
It accuses him of kidnapping and taking part in the murder of more than 300 militia officers. Zakayev denies those charges and a British judge has turned down Russia's request to extradite him.