A Pimco official has warned investors that President Donald Trump and Republicans most likely will only be able to pass watered-down tax-reform legislation with little economic-growth benefits.

Libby Cantrill, Pacific Investment Management Co.'s head of public policy, explained to CNBC that getting reform enacted is very difficult. "At the end of the day, if we see any action on tax it will likely be ‘tax-reform light.’ Some components of tax reform but for all intents and purposes more of a tax cut," Cantrill said.

"It probably won't significantly impact economic growth in 2018," she added.

Meanwhile, Treasury Secretary Steve Mnuchin on Monday vowed that the Trump administration is "100 percent committed" to getting tax reform done.

Republican lawmakers have also insisted they will make tax reform a priority, even though they are facing deadlines to increase the debt ceiling and pass a budget in September.

To be sure, Trump wants to close a frustrating 2017 with the first overhaul of the tax code in more than three decades.

Yet after seven months of work, Trump's plan remains little more than a rough sketch. Despite the haziness of the blueprint, administration officials have held to their pledges that lowering tax rates would spur the creation of millions of jobs and faster economic growth, the Associated Press reported.

The White House maintains that the House and Senate will begin considering a detailed tax overhaul after the August recess with final passage scheduled for November. But after the Republican drive to repeal the 2010 health care law collapsed this summer, Senate Majority Leader Mitch McConnell declared that the president had "excessive expectations about how quickly things happen in the democratic process."

Pimco isn't alone in becoming pessimistic about the Trump administration.

Goldman Sachs also isn’t holding out much hope for Trump’s much-touted and long-promised corporate-tax reform.

“We continue to believe a tax cut is slightly more likely than not, but our conviction is low, as there has been little progress to date,” Goldman analyst Alex Phillips wrote in a note, the New York post reported.

“If tangible progress has not been made by October, after these fiscal deadlines have passed, tax legislation will start to look less likely, in our view.”

Recent White House turmoil has raised more investor questions about the Trump administration's ability to implement its pro-growth agenda, Reuters reported.

“Picking fights and getting criticized by members of one’s own party don’t help in pursuing one’s agenda,” Peter Boockvar, chief market analyst at The Lindsey Group, wrote in a note to clients Friday, Bloomberg reported.