Tusk met May at her office at 10 Downing Street as negotiators for the two sides held a fourth round of Brexit talks in Brussels.
The meeting comes days after May proposed a two-year transition period to smooth Britain's departure from the bloc.
May hopes her proposal which would see Britain abide by EU rules and pay into its coffers for two years after Brexit in March 2019 will help persuade EU officials to move talks past terms of the divorce and onto future trade and security relationships.
The EU says it won't discuss future relationships until it has guarantees on Britain's outstanding financial commitments, the rights of EU and British citizens affected by Brexit and the status of the Irish border.
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EU leaders are scheduled to assess at an October 19-20 meeting whether Britain has made "sufficient progress" on the divorce arrangements for negotiations to move on.
Meanwhile, British Foreign Secretary Boris Johnson tried to reassure eastern Europeans that they will remain welcome after Brexit. When Britain leaves the bloc it will end the automatic right of EU nationals to live and work in the UK, and that has left many worried for their futures.
"We would be crazy to let them go back to Romania, we want to ensure ... their rights are protected," said Johnson, who is on a visit to the Czech Republic, Romania and Slovakia.