Rishi Sunak's flagship bill to eventually ban smoking looks set to be shelved after he called a surprise July general election.
The prime minister would not guarantee the law would pass before Parliament shuts down for the election on Friday.
Talks between the government and opposition parties over which bills to rush through before then are ongoing.
Labour has previously pledged to bring in the ban if it wins power at the election on Thursday 4 July.
Mr Sunak also remains committed to creating a "smoke-free generation" and the ban is likely to feature in the Conservative manifesto.
The proposed law would prevent anyone born after 2009 from legally smoking by gradually raising the minimum age to buy cigarettes from the current level of 18.
'Absolutely nuts'
In an update to MPs, Commons leader Penny Mordaunt did not include the bill among those currently scheduled to be debated before Friday.
Speaking to the OceanNewsUK in Wales, Mr Sunak declined to say whether the bill would be included.
"I will do everything I can to move these things forward, but it is dependent on the co-operation of other parties," he added.
The bill only began its journey through the House of Commons last month. It is yet to be debated in the House of Lords, which makes it more difficult for it to be passed quickly.
Under the government's plan, the age rises were not due to begin until 2027. It would not affect those who can currently buy cigarettes.
It has faced a backlash from Tory MPs, with 58 of them, including some of Mr Sunak's ministers, voting against it in the Commons last month after the PM granted them a free vote.
Ex-prime minster Boris Johnson has also led Tory opposition outside Parliament, branding the plan "absolutely nuts".
'Wash up'
A victims bill that authorises payments to those affected by the infected blood scandal looks set to pass in the accelerated process to endorse bills, known as the "wash-up".
The government has announced that the House of Lords will debate the Leasehold and Freehold Reform Bill on Friday, meaning it may become law before the dissolution of Parliament.
Legislation to pay compensation to victims of the Post Office Horizon scandal was passed by Parliament on Thursday evening.
But bills that are at risk include legislation to deliver a Tory manifesto promise to ban "no fault" evictions in England, and set up a regulator for English football.
Mr Sunak highlighted the smoking ban in his speech announcing the election on Wednesday, in a signal it would feature in the Tory election manifesto.
He said: "We will ensure that the next generation grows up smoke free."
It would have eventually made the UK the first country in the world to ban adults from buying tobacco, and had been seen as a political legacy for Mr Sunak if the Tories are not re-elected.
