Russian tennis player Vera Zvonareva was blocked from entering Poland on Friday "for reasons of state security and public safety".
The former world number two, 38, was on the list of players set to compete at the Warsaw Open, starting on Monday.
But Poland's interior ministry said she is also on a list of people considered "undesirable" in the country.
Poland has become one of Ukraine's staunchest allies since it was invaded by Russia in February 2022.
The country has been refusing entry to people who support the actions of Russia and Belarus, however, Zvonareva had 'no war' written on her visor hat while playing at the Miami Open in March 2022.