Chelsea fans must stop the "completely inappropriate" chanting of Russian owner Roman Abramovich's name, British Prime Minister Boris Johnson's spokesman said on Monday.
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Blues supporters again expressed their backing for Abramovich during Sunday's home victory against Newcastle, after he was sanctioned by the British government last week as part of its response to Russia's invasion of Ukraine.
Abramovich's assets were frozen, with Chelsea placed under a special licence which allows them to operate but unable to generate new revenue.
The billionaire, described by the UK government as part of Russian President Vladimir Putin's inner circle, has brought unprecedented success to Chelsea since he bought the club in 2003.
But Johnson's spokesman said it was time for the chanting to stop.
"We recognise the strength of feeling around people's clubs but that does not excuse behaviour which is completely inappropriate at this time," he said.
"I think people can show passion and support for their club without resorting to that sort of stuff."
Abramovich put the Premier League club up for sale on 2 March and a number of interested parties are understood to remain in the frame despite the imposition of sanctions.
These include British billionaire Nick Candy, a consortium featuring Los Angeles Dodgers part-owner Todd Boehly and Swiss billionaire Hansjoerg Wyss, plus interest from former Liverpool chairman Martin Broughton.
The government has said it is still "open" to Chelsea being sold but that a new application would be needed to enable a sale.
So far, the prime minister's spokesman said, the club had not applied for a variation to its strict special licence.
The government will oversee the sale process to ensure there is no benefit to Abramovich, with New York merchant bank the Raine Group handling the process.