(CNN) He's a former alcoholic, an ex-soccer player and he doesn't have a university degree.

Martin Schulz is not your average candidate for Chancellor.

But on September 24, the votes of millions of Germans will decide whether he will replace Angela Merkel, Germany's leader since 2005.

Like America's Bernie Sanders and the UK's Jeremy Corbyn, he's a male social democrat taking on a more conservative female politician. And according to the polls, Schulz's chances don't look good.

Could he do what Sanders and Corbyn failed to? Here's what you need to know about Merkel's challenger.

Schulz the man

Sanders and Corbyn were both viewed as outsiders trying to break into and shake up mainstream politics. And Schulz's early life certainly doesn't look like that of a typical career politician either.

A serious knee injury shattered his childhood dreams of becoming a pro soccer player. He struggled with alcoholism and never went to university, working in a bookstore instead and later becoming mayor of his local town.

It's a past he's happy to discuss. "When I left school early I really hit rock bottom," he said during a live YouTube interview with German voters on Tuesday. "That was the beginning of a crisis in my life."

Schulz has been holding campaign rallies across Germany -- often attracting thousands -- in the run-up to the election.

But for the past six years he's been president of the European Parliament -- and was a member of it for 16 years before that.

"He's not a Corbyn or a Sanders," says Charles Lees, professor of politics at the University of Bath in England. "It's difficult for politicians who are basically insiders to suddenly adopt the mantle of the outsider without looking inauthentic."

His campaign

But Schulz did play the outsider card at the start of his campaign -- and successfully.

Support for the Social Democratic Party (SPD) surged after he became its leader in January, and the party gained 20,000 members in the months that followed.

"There was a huge amount of energy and hope among SPD supporters," recalls Andreas Jungherr, expert in political communication at the University of Konstanz in southern Germany. "Schulz was trying to use similar rhetoric to Sanders and Corbyn -- the rhetoric of hope and optimism."

Countless memes were spawned, including a riff on the Obama "hope" poster and calls to "Make Europe Great Again."

Schulz's election as leader of the SPD spawned the "MEGA" meme ("Make Europe Great Again"), riffing on President Donald Trump's campaign slogan.

Key to the successes of Sanders and Corbyn was a strong grassroots campaign -- and that's vital to the SPD's efforts too.

Tobias Nehren, who heads up the SPD's digital campaign, spent several weeks in the US before last year's election, getting top tips from activists who worked for Sanders and his rival Hillary Clinton.

In recent months, he's been working to get the SPD's new online supporters out on the streets, knocking on millions of doors.

And like Sanders and Corbyn, Schulz has raised most of his campaign finance from a huge number of small donations.

But lack of money is a problem and Schulz has lost his early momentum, falling back in the polls and turning away from visionary rhetoric towards more concrete policy proposals.

In Tuesday's YouTube appearance, it was the old Schulz who turned up -- idealistic and impassioned, relaxed and candid: "a man of the people," as one Twitter user wrote

"Authentic, likeable, modern, competent, persuasive, with clear ideas and structure. @MartinSchulz you are my chancellor!" wrote another Twitter user Mc Fly.

His opponent

A big part of Schulz's problem is his opponent, argues Lees.

"He's up against a much more accomplished political operator than Corbyn was at the last election and arguably also Bernie Sanders," he said.

"Merkel has got fantastically attuned political antennae."

She rarely mentions Schulz's name on the campaign trail and is often accused of avoiding controversial issues and failing to present concrete policies.

Those tactics also make it hard for Schulz to launch a successful attack.

The two candidates took part in a live television debate three weeks before the election.

"There is plenty of substantive ground to criticize Merkel," argues Dan Hough, professor of politics at the University of Sussex in England.

"But unless she does something to show her incompetence, Schulz will struggle," he says. "And the historical record shows she doesn't do that very often."

A televised "duel" between the two candidates Sunday was widely seen as Schulz's chance to rattle his rival and position himself as a realistic alternative.

But the few blows he managed to land -- on Merkel's refugee policy, the diesel scandal and crime -- did little to unsettle her.

The voters

Sanders and Corbyn were both appealing to an electorate unhappy with the status quo, fed up with years of austerity and sharp-suited, silver-tongued career politicians.

Although Schulz is preaching a similar message -- against inequality and worker exploitation, for state investment and social justice -- it doesn't seem to be cutting through.

"Unlike in [other] Anglo-Saxon economies, ordinary voters are pretty content," argues Lees. "It's not an unhappy electorate."

There are problems, but they're not very apparent, he explains.

Moreover, German voters "tend to have a strong aversion to political risk because of the country's history."

Germany's post-war history seems to bear that out. The country has had only eight different leaders since 1949 -- and three of them have been in office for at least 12 years.

The system

While both Sanders and Corbyn were essentially in a straight-up fight for power with their more conservative rivals, Schulz is working within a more complicated multiparty system.

That hampers him -- and his cause -- in two ways.

German governments are nearly always formed by coalition -- and Schulz's Social Democrats have been ruling alongside Merkel's Conservatives for the past four years.

"If he starts criticizing Merkel's government, he's criticizing his own party," Hough points out. "His room for maneuver is pretty slim."

An SPD supporter holds up a "Now Is Schulz" poster at a campaign rally.

The multiparty system also means that genuine political renegades are more likely to find homes in smaller, niche parties away from the center ground.

That's where discontented voters will be drawn too. "The existence of a left-wing party is something Corbyn and Sanders never had to deal with," explains Hough.

"I cannot think of anybody in the SPD who would have a realistic chance of doing a better job than Martin Schulz," he says. But winning the election is a tough ask.

"He needs to find an angle on Merkel that works. He hasn't done that so far."