"Currently, 41 percent of US adults say they have a favorable opinion of the Democratic front-runner, while 51 percent hold an unfavorable view," Gallup said in a press release.
Clinton faced similar poor popularity ratings back in 1992, but they were mainly caused by the American public’s lack of familiarity at the time, the release recalled.
"By contrast, her current 41 percent favorable rating is arguably her worst, given her nearly universal name recognition," Gallup pointed out.
Clinton was most popular among Americans in 1998 after her husband, former President Bill Clinton, was impeached when her rating hit 67 percent, but it fell back to 44 percent after he stepped down as president, the release added.
"As secretary of state in [President] Barack Obama's administration, her favorability rating never fell below 60 percent," the release noted. "But upon leaving her cabinet post and returning to the political fray, Clinton saw her marks begin a downward slide."
Ominously for Clinton, the Gallup release compared her unfavorable ratings now to those she experienced during her unsuccessful presidential campaign against Obama for the Democratic presidential nomination in 2008.
However, Clinton remains much better liked among Democrats than any of her current competitors for the nomination, the release said.
Clinton’s main challenger, Senator Bernie Sanders, enjoys 46 percent favorable ratings, a seven point rise from the polling he received from July 8 to July 21.
"Nonetheless, if Clinton's national image problem persists, this may cause concern for Democratic voters looking to back a nominee who can win the general election," the release warned.
The poll was carried out by phone from August 19 to September 1 with a random sample of up to 1,000 US adults identifying as Democrats, living in all 50 states.