"I am realistic and I think that first of all we have to work out a new return policy, which would be a policy of sending them back," Tusk said in an interview with Polska The Times daily.
He also stated that the European Union is unable to allow every migrant asking for a residence permit to remain in its member states.
"Those who say let's open the door widely are cynical, because they know it is not possible. In a responsible manner we can talk about welcoming only a defined group of immigrants."
The remark follows a European Commission proposal to take in 20,000 refugees over the next two years, distributing them among EU member states.
The final quotas will be set depending on population, GDP, the unemployment rate, and the number of immigrants already legally hosted by the country.
The most recent tragedy took place in April, when a boat with some 900 migrants, on course from Libya to Italy, capsized in the Mediterranean Sea, killing almost everyone on board.