What is May 9?
May 9, known as "Victory Day" inside Russia, commemorates the Soviet Union's role in defeating Nazi Germany in World War II.
Victory Day is marked by a military parade in Moscow, and Russian leaders traditionally stand on the tomb of Vladimir Lenin in Red Square to observe it.
"May 9 is designed to show off to the home crowd, to intimidate the opposition and to please the dictator of the time," said James Nixey, director of the Russia-Eurasia Programme at Chatham House told CNN.
Western officials have long believed that Putin would leverage the symbolic significance and propaganda value of the day to announce either a military achievement in Ukraine, a major escalation of hostilities -- or both.
The Russian president has a keen eye for symbolism, having launched the invasion of Ukraine the day after Defender of the Fatherland Day, another crucial military day in Russia.
Preparing for mobilization?
Putin has many options on the table, according to Oleg Ignatov, senior analyst for Russia at Crisis Group. "Declaring war is the toughest scenario," he said.
Another option for Putin is to enact Russia's mobilization law, which can be used to start a general or partial military mobilization "in cases of aggression against the Russian Federation or a direct threat of aggression, the outbreak of armed conflicts directed against the Russian Federation."
That would allow the government not just to assemble troops but also to put the country's economy on a war footing.
Russian forces have lost at least 15,000 soldiers since the beginning of the war, according to Nixey, and reinforcements will be needed if Moscow is to achieve its goals in Ukraine.
Mobilization could mean extending conscription for soldiers currently in the armed forces, calling on reservists or bringing in men of fighting age who have had military training, said Ignatov.
But it would also represent a big risk for Putin.
"It would change the whole Kremlin narrative," said Ignatov, noting that the move would force Putin to admit that the invasion of Ukraine has not gone to plan. Full-scale mobilization could also damage the struggling Russian economy, he said.
"If they declare full-scale mobilization, some people wouldn't like it," said Ignatov.
Putin could also impose martial law in Russia, suspending elections and further concentrating power in his hands, Ignatov said.
This would impose rules such as restrictions on men of fighting age leaving the country, which could also prove unpopular, he added.
What else could happen?
If Putin doesn't declare war, he may look elsewhere to make a statement to mark Victory Day.
Other options include annexing the breakaway territories of Luhansk and Donetsk in eastern Ukraine, making a major push for Odesa in the south, or declaring full control over the southern port city of Mariupol.
There are also indications that Russia could be planning to declare and annex a "people's republic" in the southeastern city of Kherson.
However it is hard to predict what Russia and its president will do, the analyst added.
"All the decisions are made by one man and a couple of his advisers," said Ignatov.
Yet US State Department spokesman Ned Price said Monday there is "good reason to believe that the Russians will do everything they can to use" May 9 for propaganda purposes.
"We've seen the Russians really double down on their propaganda efforts, probably, almost certainly, as a means to distract from their tactical and strategic failures on the battlefield in Ukraine," Price said at a State Department briefing on Monday.