Daniil Medvedev and fellow Russian tennis stars could be banned from playing at Wimbledon unless they denounce president Vladimir Putin.
That was confirmed by UK sports minister Nigel Huddleston on Tuesday, as he told a parliamentary committee there were concerns about Russian representation in sport.
With Russia's military invasion of Ukraine ongoing, Huddleston warned it would not be appropriate for anyone to be seen to be flying the flag for their homeland, or showing any support for Putin's regime.
Speaking at a Digital, Culture, Media and Sport Committee session, Huddleston was asked about Wimbledon and Medvedev, the current men's world number one player and reigning US Open champion.
Huddleston said: "We are looking and talking to various sports about this and what the response and requirements should be there. Absolutely, nobody flying the flag for Russia should be allowed or enabled."
He added: "We need some potential assurance that they are not supporters of Vladimir Putin and we are considering what requirements we may need to get some assurances along those lines.
"In short, would I be comfortable with a Russian athlete flying the Russian flag? No."
Asked about the All England Club, which hosts Wimbledon, Huddleston said: "We are in discussions."
Russia has four players in the men's top 30, and three in the women's top 30.
They are playing under neutral flags at present, after the ATP and WTA tours decided Russian and Belarusian players should not be permitted to represent those nations while conflict continues in Ukraine.
Wimbledon runs from June 27 to July 10 this year, with a week of qualifying preceding the tournament.
Demanding each player from Russia directly comes out against president Putin would be going a step beyond what is currently required.
Huddleston said: "We are looking at this very issue about what we do with individuals, and we are thinking about the implications of it, because I don't think people would accept people very clearly flying the Russian flag, in particular if there is any support and recognition for Putin and his regime."
Speaking last week at Indian Wells, Medvedev spoke about being allowed to continue to play on the tour.
"It's definitely not for me to decide. I follow the rules. I cannot do anything else," he said. "Right now the rule is that we can under our neutral flag.
"I want to play my favourite sport. Until I have the chance to do it, I'm going to be there to try to play for the fans, play for other people, for myself also of course.
"Also I think tennis is a very individual sport, so far what we are seeing [being sanctioned] are more national teams or some team sports. Let's see how the situation evolves."