WASHINGTON, US (Reuters) - Republicans in the Senate scrambling on Monday (Sept 25) to salvage a last-ditch effort to repeal and replace the Affordable Care Act.

A bill put forward by Senators Lindsey Graham and Bill Cassidy teetering on the edge of collapse.

"I'm really concerned about continued coverage and protection for people with pre-existing conditions. This bill clearly weakens those protections," US Republican Senator from Maine, Susan Collins said.

She is one of at least three members of her party to voice concerns with the bill.

Republicans need to muster at least 50 Senate votes behind the effort. They control 52 seats in the Chamber.

The math does not look good.

The Graham-Cassidy bill would strip federal funding from the Medicaid programme for the poor and disabled and cut subsidies created under Obamacare.

It would instead give money to individual states as block grants to fund their healthcare needs as they see fit.

The American Medical Association, the health insurance industry, and the AARP all coming out against it.

The Washington Post reporting that Republicans plan to release a revised version of the bill on Monday, sending more federal aid to Alaska and Maine, the states of two holdout senators.

The Congressional Budget Office could release a preliminary analysis of the bill's cost this week.

The Senate Finance Committee is meeting Monday in an effort to build support for the bill.

Republicans have repeatedly failed at efforts to repeal Obamacare, despite campaigning against it for seven years.

They are running out of time.

On Saturday, a procedural window closes, meaning that afterward they will need sixty votes in the Senate to legislate.

Right now, it is uncertain they can muster fifty.