The All England Club and the Lawn Tennis Association reversed last year's ban on competitors from the two countries following the invasion of Ukraine but there appears a chance some may not make it anyway.
Sixteen-year-old Mirra Andreeva is due to make her Wimbledon debut in qualifying but said after losing to Coco Gauff in the third round in Paris on Saturday that she was still waiting to be granted a visa.
Australian Open champion Aryna Sabalenka has also spoken about not having received her visa while world number two Daniil Medvedev pointedly said "if I'm able to come to UK to play Wimbledon" when talking about the grass-court season.
The Home Office is carrying out additional checks on Russian and Belarusian nationals, extending a wait that is currently at least six weeks, while fast-track options are not available to people from the two countries.
Wimbledon begins on July 3 and, speaking after reaching the French Open quarter-finals, Russian Karen Khachanov, who still has a visa from previous years, said: "I heard that it takes much longer to issue the visa."
Under normal circumstances, Andreeva would be a strong candidate for a Wimbledon wild card, but it appears hugely unlikely the All England Club would offer such help at the moment.
Fellow Russian Anastasia Pavlyuchenkova, meanwhile, is set to miss the tournament because she is not currently ranked high enough to get into the main draw or qualifying.
Pavlyuchenkova is a former French Open finalist but was sidelined long term following knee surgery.
She is showing strong form in Paris, making it through to the quarter-finals, and was asked whether she could seek a wild card.
Pavlyuchenkova said incredulously: "Are you serious? Do you think after the situation last year they would give me a wildcard this year?"
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