The longtime leadership of Belarusian president Alexander Lukashenko "is almost over," according to one ex-Soviet specialist, as growing anti-government protests present the leader with his biggest crisis yet.

Lukashenko, who has ruled Belarus since 1994, was re-elected last Sunday for the sixth time with 80 percent of the vote. However, protesters rejecting the poll's legitimacy have taken to the streets, with tens of thousands of Belarusians rallying in the capital of Minsk on Sunday, demanding that he step down.

For Nikolai Petrov, an ex-Soviet specialist at Moscow's Higher School of Economics and a senior research fellow at London's Chatham House, the writing is on the wall for the longtime leader. 

"He lost the support of his people," Petrov tells CGTN Europe. "He is not supported by the West and by Russia. So I can hardly imagine how it would be possible for him to survive this crisis."

Read more: Belarusian leader says no to new election, accuses NATO of build-up

Even so, the 65-year-old president has dug in over the week, responding to the mass protests with a swift crackdown. Around 7,000 demonstrators have been arrested, with reports of torture being used against those detained.

During a pro-government counter-protest on Sunday, Lukashenko remained defiant, rejecting calls to step down, blaming external forces for discontent at home.

"I called you here not to defend me... but for the first time in a quarter-century, to defend your country and its independence," the leader told a Minsk crowd of at least 10,000 people.

Pictures: Belarus protests

However, the president's appearance at the protest is a further sign of weakness, says Petrov: "I think that now Lukashenko is not even one of the players to discuss how exactly the crisis can be fixed. 

It was clearly seen today when he came to speak at the meeting for the first time ever – his speech was not even shown by state television because it's on strike. It looks like he lost support of the state apparatus."

However, growing discontent among the Belarusian army and media haven't stopped Lukashenko reaching out to Russia, Belarus's closest ally, for support.

Following a telephone conversation with president Vladimir Putin, the beleaguered leader claimed that Moscow had promised help to him "ensure the security of Belarus."

There has even been speculation that there could be a Russian military intervention, as seen in Ukraine in 2014, particularly with the European Union readying sanctions against the current Minsk administration. 

However, Petrov says Moscow is unlikely to come to Lukashenko's rescue. 

"I think this is not very probable, although nothing can be excluded," he stated. 

Read more: Belarus releases 2,000 protestors but denies abuse

For Petrov, Belarus and Ukraine are different ballparks: Belarusian politics doesn't have the same geopolitical dimension as Ukraine.

"The clash between Russia supporters and West supporters is almost absent," he says. "It's much more rational for the Kremlin to negotiate with the next leader of Belarus about keeping pretty close, friendly relations than to invest in supporting an unpopular leader."

If anything, he says Lukashenko's criticisms of Russia during his presidential campaign lost him support in Moscow and some of his traditional base at home.

For most Belarusians and likely now for Putin, "it's only about replacing the old and old-fashioned leader with the new one," says Petrov. "It's more about whether the Belarusian society and Belarusian elites are capable now to reach any kind of agreement, how to move forward and to organize a kind of round table and to agree about next president."