Spiro added that "as far as reforms are concerned", Sarkozy "did nothing" during his five years as president, so his economic credibility lies "in tatters".
Meanwhile, Sarkozy will have to contend with a stronger far-right Front National party, which has strengthened in the past couple of years under its new leader, Marine Le Pen.
"How he deals with the challenge of Le Pen is absolutely crucial," said Spiro, who forecast Sarkozy would favor a rapprochement with the far-right. At the end of his former presidency, Sarkozy hardened his stance on immigration and security issues to poach far-right voters.
Webber warned that Sarkozy's bid for presidency could have unintended consequences—namely, splitting the UMP party and the center-right vote. In which case, "Marine le Pen would have a very good chance of winning."
Victory in 2017?
A hyperactive and divisive figure reviled by many left-wing voters, Sarkozy is seen by his supporters as the only politician capable of rallying the fractured centre-right UMP party to a victory in 2017. But any political comeback could be tripped up by a series of legal troubles hanging over his head.
Sarkozy, who credits himself with having helped steer Europe through its worst economic and financial crisis since the Great Depression before being voted out, said he used his temporary withdrawal from politics to reflect and talk to ordinary French people.
"I have seen the rise, like an unstoppable tide, of disarray, rejection and anger ... Among many French people, I saw the temptation to no longer believe in anyone or anything," he said.
"This absence of all hope, so peculiar to France, now forces us to completely reinvent ourselves."
Gradually emerging as the leader of the French right in the mid-2000s, Sarkozy cast himself as a reformer with bold ideas who would break with France's past.
Read MoreCould France see the return of Nicolas Sarkozy?
His aggressive, American-style manner both attracted and repelled voters as he pledged to reform the country's labour markets and tax system to bolster industry and job creation. He stood down hundreds of thousands of strikers to raise France's retirement age to 62 from 60.
In foreign policy, he brokered a ceasefire to end a short-lived war between Russia and Georgia in 2008 and championed an international military intervention in Libya three years later.
However, a widespread public perception that he was on the side of the rich earned him the tag of "President Bling-Bling" and little sympathy with voters feeling economic hardship.
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