Work on the between London and Birmingham could be delayed by two year because of concerns about planning and financing, experts warn.
Dr Noble Francis, economics director at the Construction Products Association (CPA), predicted building work on the line would not now begin until 2020.
Bosses of HS2 Ltd immediately moved to dismiss his concerns.
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Work on the high-speed rail line has become increasingly vital to the future regeneration of Birmingham city centre, with the Birmingham Curzon Masterplan key to unlocking investment in Eastside and the Wholesale Markets area.
In its summer industry forecast, the CPA cited "concerns regarding planning and financing" as reasons why it did not think main civil engineering works would start for five years, along with people affected by HS2 also potentially causing delays through appeals.
The report states: "Due to concerns regarding planning and financing, we do not anticipate main works starting on HS2 before 2020."
Dr Francis told Construction News: "When you look at major rail infrastructure, there is usually a significant period of time before projects get off the ground.
"Thameslink was originally the Thameslink 2000, Crossrail was given the green light in 1990.
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"You won't see those sort of delays to this project but, when we are talking about major infrastructure, we as forecasters have to forecast a degree later than officially stated."
With HS2 moving and the HS2 college also to be based here, the city has become indelibly linked with the scheme.
But the line has become fundamental to wider regeneration plans, with the Midlands HS2 Growth Strategy planning to create or safeguard more than 100,000 jobs, 2,000 apprenticeships and bring about £14 billion of additional economic output.
It is also vital to transport plans in the region, with the likes of Birmingham Airport and public schemes like Sprint buses expected to be accelerated.
HS2 spokesman Richard Pain dismissed the CPA concerns, saying substantive design work, surveying and ground investigations were already under way.
"Successful planning is the key to most major projects remaining on schedule," he said.
"Following a resounding backing from Parliament at the second reading of the hybrid bill for HS2 phase one, we remain confident that the main construction of HS2 will start in 2017, with civil work to begin in 2018."
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The CPA warning comes as cross-party support for HS2 faces being thrown into jeopardy with Jeremy Corbyn heavy favourite to become Labour leader.
Mr Corbyn reportedly said the Tories' flagship transport project would turn "our great regional cities into dormitories for London businesses".
The Islington North MP was one of just a dozen Labour MPs who opposed preparatory spending on HS2 in a 2013 vote in the House of Commons.
Labour's support is important to construction work beginning, with a final vote on the legislation due this parliament.