Putin's victory is seen as a foregone conclusion.
But Boris Nadezhdin has surprised some observers by criticizing the so-called "special military operation" in Ukraine and saying he'd end it.
He says these boxes contain 105,000 signatures of support, which he submitted to the Central Election Commission on Wednesday (January 31). That should be enough to launch a challenge.
Critics say he must have the Kremlin's blessing to get this far in such a tightly controlled system.
But Nadezhdin denies that, telling reporters "Putin committed a fatal error when he started the special military operation."
Such statements have stoked speculation he's crossed a red line, and will be barred from running on a technicality or forced to drop out.
The commission has disqualified candidates in the past based on what it said were irregularities in signatures.
Nadezhdin says he's harnessing a sizeable protest vote. In Chelyabinsk last week, signatories interviewed by Reuters seemed to confirm that.
"I came because I'm against the war, and he's the only deputy against it," this woman says.
This is what Nadezhdin told Reuters last week:
"I want to change the country. I want there to be peace and normal life here, for Russia to be a peaceful and free country."
Nadezhdin sometimes appears on state TV, where he criticises the authorities before being swiftly drowned out by anchors.
After heating outages across Russia during a cold winter, he said the country would be able to spend more on its citizens if it didn't pour so much money into the military.
The Kremlin has dismissed Nadezhdin as no serious rival to Putin.
Putin has already collected more than 3.5 million signatures, according to his supporters.
