The GOP's Obamacare replacement might need some emergency treatment.

A leading House Republican on Tuesday said he has told the GOP leadership he will vote against their bill to repeal and replace key parts of the Affordable Care Act.

The loss of a vote from Rep. Fred Upton, R-Mich., the former chairman of the Energy and Commerce Committee, could make it much more difficult for Republicans to even dare to call a vote on their replacement bill, much less to get it passed this week.

Upton revealed his intention to vote against the bill during a call with a Michigan radio station. He cited the fact that a compromise amendment added to the bill last week would weaken the insurance coverage protections for people with pre-existing health conditions, which he has supported.

"This amendment torpedoes that," Upton said. "And I told the leadership I cannot support this bill with this provision in it."

"I know there are a good number of us that have raised red flags and real concerns" about the bill, Upton said. "And it's not going to get my 'yes vote' the way it is."

Republicans, who have the majority of House members, have struggled for almost two months to convince several dozen members of their own caucus to vote for the bill, dubbed the American Health Care Act.

Democrats are uniformly against the bill, meaning that the GOP can afford only around 22 defections. With the loss of Upton, there are at least 20 current "no" votes, and another 18 or so undecided Republicans, some of whom are leaning "no."

Despite White House claims that a vote on it, and passage, could come this week, House Speaker Paul Ryan has held off calling for a vote, because of those holdouts in his caucus. In late March, Ryan and President Donald Trump agreed to yank a prior version from a planned vote because it was headed to failure.

Moderate GOP members, as well as some others, fear that the bill could lead to much-higher insurance premiums for some Obamacare customers, particularly those with pre-existing health conditions.

Those fears were reinforced last week when House conservatives won changes to the bill to allow states to get waivers for insurance plans that charge people with pre-existing conditions more for coverage if the state has a high-risk insurance pool.

Ryan insisted Tuesday that there were adequate protections for people with such existing health problems in the bill.

But a Health Affairs Blog article posted Tuesday warned that the use of a high-risk pool to cover people with pre-existing conditions "would not be enough to solve the problems created by eliminating" several protections now in Obamacare.

"The number of people affected by peeling back these policies would be much larger than could be effectively accommodated in high-risk pools, given the levels of funding offered in recent legislative proposals," said the article by Linda Blumberg and John Holahan of the Urban Institute.

House Majority Whip Rep. Steve Scalise, R-La., walked away from reporters at the end of a news conference Tuesday without answering their called-out questions about what the "whip count" was. A whip count is a tally of the number of congressmen who intend to vote "yes" or "no" on a bill, along with the number of undecided members.

Rep. Joe Crowley of Queens, New York, the leader of the House Democratic Caucus, said the current version of the Republican bill, like the original one introduced nearly two months ago, "would still take away" insurance coverage from 24 million Americans who currently have insurance.

Crowley said the Republican holdouts "recognize" the damage the bill would do both to those millions of people, as well at to people with health issues who continue being insured at a much higher cost.

He also said that Republicans "can't run away from this vote" because it is their leadership who would be calling for the bill to be voted on, not the Democrats.

"There's no running away from this," Crowley said.

Correction: The Republicans' original bill to repeal and replace Obamacare was introduced nearly two months ago. An earlier version misstated the timing.