© Getty
Meanwhile planned campaign stops have been dropped by the presidential candidate as she modifies her schedule following doctor's orders.
The 68-year-old was rushed out of a 9/11 commemoration service today suffering from a "medical episode", according to a law enforcement witness.
A video later emerged of the Democratic presidential nominee, showing the dramatic moment when her "knees buckled" and she nearly crumpled to the pavement while waiting for a car to collect her.
Now sources have claimed Democratic Party insiders are rushing to consider a replacement candidate in light of Mrs Clinton's poor health.
Emmy Award winning New York Journalist and MSNBC pundit David Shuster tweeted: "Clarification from dem operatives @HillaryClinton pneumonia: Expect emergency DNC meeting to CONSIDER replacement."
But a senior democrat has revealed that while the committee may "plead" with Ms Clinton for her to step down, the decision is ultimately down to her.
A top source in the party reportedly said: "We can make contingencies, argue, plead with Hillary Clinton, but DNC bylaws are clear - her nominee status is now totally up to her."
The campaign has confirmed that Ms Clinton will not attend scheduled campaign stops in California over the next two days, with no comment on events after that.
Lisa Bardack, Clinton's doctor said: "Secretary Clinton has been experiencing a cough related to allergies. On Friday, during follow up evaluation of her prolonged cough, she was diagnosed with pneumonia. She was put on antibiotics, and advised to rest and modify her schedule. While at this morning's event, she became overheated and dehydrated. I have just examined her and she is now re-hydrated and recovering nicely."
Mrs Clinton's diagnosis came three days before today's medical episode, Dr Bardack said. Her campaign team said she had been "overheated" but was now feeling "much better".
She later emerged from her daughter's New York residence and tried to reassure people outside, saying "I'm feeling great. It's a beautiful day in New York"
US journalist Rick Levanthal of Fox News said: "She unexpectedly left early because of what appeared to be a medical episode.
"I have a law enforcement source who was there, who was 15 feet away form Hillary Clinton. He said she was standing on a curb with her protective detail waiting for her motorcade.
"They were surprised to see her because she wasn't meant to be leaving yet.
"When it finally rolled up my source said she stumbled off the curb, appeared to faint, lost one of her shoes, which wound up under the van."
Express.co.uk have contacted The Democratic National Comittee for comment.
Now zoomed-in footage has emerged of Mrs Clinton's foot as she is bundled into the back of the blacked-out car.
It appears to show her legs are completely limp, leading to speculation online that she was completely unconscious when she was led away by her staff.
SHE DID NOT JUST STUMBLE coming off of the curb.
If all she had was allergies and pneumonia there would be no talk of trying to get her to step down as nominee.
Is the poo hitting the fan?