The former chairman of HS2 has been appointed by Boris Johnson to lead a review of the planned high-speed rail line.
Douglas Oakervee, who spent almost two years in the post after his appointment in March 2012, will head up the project which will examine the case for building the new line.
Mr Johnson is currently vying to become the next Tory leader and Prime Minister.
He said: "I have already asked provisionally Douglas Oakervee, who was the original chair of Crossrail, to have a look at the business case for HS2 and to think about whether and how we proceed."
But Mr Johnson, who has been a critic of HS2 in the past, also made it clear that he would be reluctant to cancel the project outright.
He said: "I worry about cancelling a big national project of that scale without anything else to replace it."
Trains are due to start running on HS2 between London and Birmingham by 2026 and then onto the East Midlands, North West and Yorkshire by 2033.
Mr Johnson floated the option of "re-profiling the spend" so that construction of the northern leg of HS2 and the Northern Powerhouse Rail scheme - a proposed rail line between Leeds and Manchester - became the top priority.
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And he said that, as Prime Minister, he hoped to improve transport infrastructure in the North and West Midlands just as he improved transport in London as city mayor.
Mr Johnson said: "I would like to be the Prime Minister who does for connectivity in the West Midlands and the Northern Powerhouse what I did for London, with Crossrail and with massive tube upgrades."
He was speaking over the weekend at a private hustings in the capital for Conservative Party constituency chairs.
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Mr Johnson is one of six candidates still in the race to replace Theresa May as party leader and Prime Minister.
Supporters of HS2 have been concerned that the project could become a victim of the Conservative leadership contest, particularly as Mr Johnson has appeared to be highly sceptical about it in the past.
City leaders from across the Midlands and the North are campaigning to put pressure on Tory candidates to confirm they will press ahead with HS2 and are to gather in Birmingham on Wednesday to show support for the scheme.
A damning report by a House of Lords inquiry found in May that HS2 was unlikely to be built within the current £55.7 billion budget, saying the costs did not appear to be under control.
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But Mr Johnson's comments suggested that, while there may be changes if he became Prime Minister, the scheme was unlikely to be cancelled outright.
Speaking at the hustings, he said: "I’ve got to be realistic. As Prime Minister of a great economy, I’d have to think very very carefully about instantly cancelling a huge national infrastructure project.
"I'd have to look very carefully at the business case. Now, I happen to think the business case for HS2 is by no means as good as it should be.
"The costs seem to be spiralling out of control.
"But I have to think very hard about the experience of the 海角视频 in cancelling big infrastructure over the last 60 years or so.
"This is a country that needs fantastic infrastructure."
Mr Johnson said he believed the Government should be focusing on improving transport infrastructure in the North, adding: "On Crossrail of the North, on Northern Powerhouse Rail - we should be looking at connectivity in the West Midlands."
Mr Johnson told his audience: "So what I would say about HS2 is, it’s time for a proper review.
"It may be, talking to friends in the Treasury, that at the very least it is time to start thinking of re-profiling the spend so as to begin in the north, to invest first in Northern Powerhouse rail and to do it that way round.
"What I would like to do is get a proper view by a world-acclaimed expert.
"I worry a great deal about HS2 but I also worry, as someone who believes in infrastructure, about cancelling a big national project of that scale without anything else to replace it."