• The Russians have sustained more casualties than expected, but are still "advancing steadily," said Niall Ferguson of the Hoover Institution.
• "The assumption that this is going to drag out, that the United States can sit back and watch the economic sanctions do their work may be gravely mistaken," Ferguson said.
• Sanctions may be able to change Putin's behavior down the road, but cannot be used to stop the violence, said Anna Ohanyan of the Carnegie Endowment for International Peace.

The strategy of sitting back and waiting for Russia's war machine to grind to a halt because of sanctions could go "terribly wrong," according to Niall Ferguson, a senior fellow at the Hoover Institution at Stanford University.

"It's a highly risky strategy," he said.

The Ukrainian resistance cannot hold the fort for much longer, and sanctions by the West won't be able to stop Russia in time, he told CNBC's "Squawk Box Asia" on Friday.

He said the U.S. is relying heavily on sanctions and "very belated arms deliveries" to Ukraine, but he's concerned that those fighting for Ukraine won't be able to defend the country for long.

Though the Russians have sustained more casualties than expected, they are still "advancing steadily," he said.

"The assumption that this is going to drag out, that the United States can sit back and watch the economic sanctions do their work may be gravely mistaken," Ferguson said.

Anna Ohanyan of the Carnegie Endowment for International Peace (CEIP) echoed that sentiment.

"While the sanctions will start biting — perhaps can change Putin's behavior down the road — at this point, they cannot be relied on as an instrument to be used to stop the violence," said Ohanyan, a nonresident senior scholar in CEIP's Russia and Eurasia program.

"It won't work fast enough to avert a Russian victory in Ukraine and I think this is the critical problem," Ferguson said.

'Nightmare scenario'

The U.S. and its allies have imposed wide-ranging sanctions on Russia for its invasion of Ukraine. But it appears that there's a race between Russia's military advancements and the sanctions that are crippling Moscow.

"There's no guarantee that Ukraine holds out, and what I dread is steadily worse news from Ukraine, and the breakdown of Ukraine's defenses," Ferguson said.

"We'll sit there saying, oh, well the sanctions have really hurt Russia — but it won't matter to Putin because he will be able to claim victory. That for me is the nightmare scenario," he added.

Ferguson said the U.S. should help support Ukraine's defenses without escalating it into a full-blown NATO-Russia war.

Arms deliveries to Ukraine slowed down previously, and now there is a "frantic effort" to help Ukraine keep up the fight, he said.

That, however, may create the conditions of a proxy war, CEIP's Ohanyan said.

"It appears that unfortunately, [at] this point, sanctions and the military assistance work at cross purposes," she said.

Opportunity for a deal

Ferguson also said the U.S. is "missing an opportunity" by leaning on sanctions.

He said he believes that a deal can be made between Russia and Ukraine if Kyiv is willing to accept neutrality and take NATO membership off the table.

He pointed to a 2014 proposal that former U.S. Secretary of State Henry Kissinger published, presenting the idea of Ukraine being a neutral country instead of attempting to join NATO.

"It is clear that President Zelenskyy is open to that idea, which is a major shift in Ukraine's position for the sake of trying to save his country from further destruction," he said.

Ukraine President Volodymyr Zelenskyy this week told ABC News that he has "cooled down" regarding the question of joining NATO.

He said Ukraine understands that NATO doesn't want to accept it into the alliance, and the country will not beg to be allowed into NATO.

Peace is "urgently needed" to avoid continued bloodshed and the destruction of Ukraine, which Ferguson said seems to be the Russian plan for now.

"The goal was to prevent Ukraine being a successful democracy oriented towards the West, whether in NATO or the EU," he said. "You can achieve that just by destroying Ukraine's infrastructure and turning it into a smoking pile of rubble and unfortunately, every passing day allows President Putin to do more of that," he said.

Ohanyan agreed that there has to be a diplomatic push to de-escalate, start a cease-fire and negotiate on "bigger issues."