Russian and Belarusian players fear they could miss Wimbledon because of delays in getting UK visas.
The All England Club banned them from competing last year following Russia's invasion of Ukraine, which was supported by Belarus.
They can compete this year but must sign declarations indicating their neutrality.
The Home Office said applicants have to undergo "thorough checks" before permission to enter the UK is granted.
Wimbledon takes place in London from 3-16 July.
Sixteen-year-old Russian Mirra Andreeva, who had impressive runs at the Madrid Open and the French Open, said she is still waiting to see if she can play at the tournament.