• On Thursday No 10 said Mr Sunak was not expected to attend "due to other pressing domestic commitments including preparations for the autumn Budget".
• However, the announcement prompted criticism, including from the UK's COP26 president, Tory MP Alok Sharma.
Prime Minister Rishi Sunak could still attend the COP27 climate summit, sources have told the BBC.
The prime minister is understood to want to attend the conference in Egypt and could go if his diary allows.
On Thursday No 10 said Mr Sunak was not expected to attend "due to other pressing domestic commitments including preparations for the autumn Budget".
However, the announcement prompted criticism, including from the UK's COP26 president, Tory MP Alok Sharma.
The UK is the current holder of the COP presidency, after hosting the summit in Glasgow last year.
The annual UN climate summits are designed to help governments agree steps to limit global temperature rises.
Mr Sharma will hand over the presidency to Egypt at the COP27 summit in Sharm el-Sheik, which takes place from 6 to 18 November.
The conference finishes the day after Chancellor Jeremy Hunt is due to set out the UK's tax and spending plans in his highly anticipated autumn statement.
Asked on BBC Breakfast whether the prime minister could attend, Environment Minister Mark Spencer said Mr Sunak had "a huge inbox", with challenges including the economy and rising global energy and food prices.
"His focus at the moment is dealing with the autumn statement and the government's response to those global challenges," he said.
Mr Spencer added: "I'm sure if his diary allows he would want to go but at this moment in time don't quite know if he's going to be have time to do that.
"But rest assured there'll be serious ministers out there and big hitters because the UK's very keen to play its part in dealing with the challenges we face in the environment globally."
Asked if he would like to see Mr Sunak attend, Mr Spencer said: "If he's got time to do that."
Mr Sunak has faced criticism from opposition parties, environmental groups and some Conservatives, after No 10 said he was not expected to attend the summit.
At the weekend Mr Sharma, who was recently demoted from cabinet, told the Sunday Times he was "pretty disappointed" at news Mr Sunak was not going, saying his attendance would signal the UK's "renewed commitment on this issue" and "allow for engagement with other world leaders".
Former Conservative chancellor George Osborne said Mr Sunak had "mishandled" the situation and questioned why he would "trash" the party's record on the environment.
Green Party MP Caroline Lucas told the BBC: "It is absolutely so wrong that Rishi Sunak is not going because the UK is still the holder of the Cop presidency. Symbols matter."
Labour and the Liberal Democrats also accused the PM of a "failure of leadership".
Meanwhile, there are reports that Boris Johnson, who attended the summit in Glasgow when he was PM, could go to Egypt for this year's event.
US President Joe Biden and France's Emmanuel Macron are also due to attend, while Mr Sunak's predecessor Liz Truss had been set to go when she was PM.
King Charles, who is a longstanding champion of environmental issues, will not attend after Buckingham Palace sought advice from then-PM Ms Truss and agreed he would not go in person. The advice has not changed under new PM Rishi Sunak.
However, the monarch will host a reception at Buckingham Palace on 4 November, on the eve of the conference, for 200 international business leaders, decision makers and charities to mark the end of the UK's COP presidency and look ahead to the summit in Egypt.
Mr Sunak will "say a few words" at the event, which will also be attended by US climate envoy John Kerry.
Teenage climate activist Greta Thunberg, who has said she will not be at the summit in Egypt, called it a "scam".
"It's very symbolic that it's being held in a tourist paradise in a country that violates many basic human rights," she told an event in London on Sunday.
"Many world leaders are too busy to go there because they have their own problems. With that mindset we're not going to be able to solve many of the problems that we face."
The Egypt conference is expected to focus on three main areas - reducing emissions, helping countries prepare for and deal with climate change, and securing technical support for developing countries for these activities.