Less than a quarter of registered voters said they support Senate Republicans' most recent effort to overhaul Obamacare, according to a poll released Thursday.

Just 24 percent of respondents approve of the healthcare reform amendment authored by Sens. Lindsey Graham and Bill Cassidy -- often called the "Graham-Cassidy bill" -- while 50 percent disapproved and 27 percent said they were not sure.

The Senate may vote on the bill as soon as next week.

Fifty-four percent of respondents said they approved of the Affordable Care Act and 63 percent said they want to keep what works and fix what doesn't, while 32 percent want to repeal and "start over" with a new healthcare law.

The Republican senators have agreed to debate Sen. Bernie Sanders, I-Vt., Monday night on CNN. Sanders introduced a socialized, "Medicare-for-all" bill last week.

Graham and Cassidy are expected to testify before the Senate Finance Committee on Monday. The bill has not yet been analyzed by the Congressional Budget Office.

Republicans have until midnight on Sept. 30 to pass the bill or lose the ability to get it through the chamber with only 51 votes as the rules for using the reconciliation tool expire. Vice President Mike Pence may cast the tie-breaking vote if needed.

The poll was conducted by Public Policy Polling, a Democratic firm based in North Carolina. The firm surveyed 638 registered voters.