After leaders held their preliminary discussion of the first post-Brexit budget, Tusk told reporters that many European heads of government were ready to contribute more money to the next budget cycle, that runs 2021-27.
"All the leaders approached [the budget] with open minds, rather than red lines," he stated.
Tusk however said that the EU Commission's ambitious deadline for reaching an agreement by the end of this year seemed "really difficult".
The EU executive wants to conclude talks by the next European elections in May 2019, however, haggling over the budget usually takes more than two years.
Germany's Angela Merkel said the debate was "constructive", and said leaders will decide how fast to move with agreeing to the EU budget after the commission's proposal will be published in May.
The German chancellor also warned cuts will have to be made to "bureaucratic" policies, like agriculture.
One of the countries that does not want to pay more after the UK leaves the EU, the Netherlands' PM Mark Rutte, said the bloc needs to modernise and reform existing programs to finds more money.
"We, in any case, do not want our contribution to rise," he said.
EU leaders also discussed the possibility of linking EU funds to migration and respecting the rule of law.
Donald Tusk told reporters the discussion was less toxic than many had speculated in the run up to the summit.
Member states that benefit from cohesion funds earlier warned against using EU money aimed for reducing economic differences across the EU for integrating migrants or for punishing countries that breach EU rules.
After the discussions Tusk said that he had only heard "positive reactions", and that the concept was not questioned by any leader who spoke.
Tusk said that Poland's premier Mateusz Morawiecki also said he was ready to support conditionality, adding that it should be built a very objective criteria.
"The possible conditionality was less controversial than expected," Tusk said - adding that the debate at this point was very general.
France's president Emmanuel Macron had a strong warning to those who infringe EU values, something Poland had been accused of by the commission.
"It would be matter of good sense to halt the payment of some [EU] funds where is there is a breach of our values," Macron said.
Read more: EU agrees budget to focus on defence, security and migration
