UK Prime Minister Boris Johnson has been warned by officials that China's President Xi Jinping is unlikely to attend the COP26 climate summit in November.
UK government sources confirmed a report in The Times that Mr Johnson had been advised the Chinese leader was not expected to come.
However Chinese officials reportedly have not ruled out a change of plans.
COP26 takes place in Glasgow from 31 October to 12 November.
Leaders from around the world will meet to discuss how to minimise global temperature rises caused by human activity.
President Xi's attendance at COP26 has long been in doubt. It is thought he has not left China since early 2020.
Government sources said Chinese officials had not been definitive about the President's travel plans and they accepted it was possible Xi could change his mind and come at the last minute to surprise the summit.
"They want to be seen as green leaders so I wouldn't rule it out," one Whitehall source said.
Diplomats said China often announced President Xi's travel plans at the last minute. One said: "We never give up hope. And we are continuing to make the case for his personal attendance."
In September, Chinese officials told Italian diplomats that President Xi did not plan to attend a meeting of G20 leaders in Rome on October 30 which immediately precedes the COP26 summit. They cited China's Covid regulations as the reason.
Western diplomats said there were genuine concerns among Chinese officials at being able to protect Mr Xi from Covid outside China.
On 19 September, the UK COP President Alok Sharma told the BBC's Andrew Marr show there was uncertainty about President Xi's attendance: "The issue of whether President Xi Jinping is going to come, that's not yet been confirmed."