Sen. Cory Booker’s presidential campaign manager is warning in a memo to staff that the Democratic senator from New Jersey must raise an additional $1.7 million by the end of the third quarter of fundraising – just 10 days away – or the campaign will not have a “legitimate long-term path forward.”

In the memo, campaign manager Addisu Demissie warned that following a weaker than expected cash haul during the early part of September, “the next 10 days will determine whether Cory Booker can stay in this race."

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The existence of the memo was first reported Saturday morning by NBC News, with Fox News confirming the news with multiple sources.

Two sources, who asked to remain anonymous to speak more freely, said it was no accident that the memo was leaked, and described it as an effort to spark a surge in fundraising over the next 10 days.

And a campaign memo sent to political reporters Saturday morning said: “This isn't an end-of-quarter stunt or another one of those memos from a campaign trying to spin the press. This is a real, unvarnished look under the hood of our operation at a level of transparency unprecedented in modern presidential campaigns.”

Booker, who declared his candidacy for the White House in early February, quickly built a formidable operation in the early voting primary and caucus states. The large staff on the ground in Iowa, New Hampshire, and other early voting states is expensive to maintain. Demissie warned that while the campaign can continue at its current size and strength, it needs more funding if it wants to expand.

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Demissie explained in his memo "If our campaign is not in a financial position to grow, he’s not going to continue to consume resources and attention that can be used to focus on beating Donald Trump, which needs to be everyone's first priority.”

While Booker qualified for the third and fourth round Democratic presidential primary debates, he’s struggled in polling, averaging in the low to mid-single digits, far behind top-tier contenders former Vice President Joe Biden and Sens. Elizabeth Warren of Massachusetts and Bernie Sanders of Vermont.

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Booker raised 4.5 million in the April-June second quarter of fundraising, far behind Biden, Sanders, Warren and South Bend, Indiana Mayor Pete Buttigieg.

Fox News' Leland Vittert and Tara Prindiville contributed to this story.