Tusk has been in Nicosia to meet Cypriot president Nicos Anastasiades, ahead of this week's European Council on migration.
"Turkish proposal still needs to be rebalanced to be accepted by EU28 but we are not there yet" said Tusk in a statement shared via his Twitter account.
"Cyprus is as important as any other EU Member State. No third country can ever be more important to me than any European Member State" he added.
"All EU actions are aimed at helping a settlement on the Cyprus issue. A settlement would be fresh start for Cyprus, Europe and wider region" Tusk said.
"Legality" and "strict conditionality"
Having underlined legality is a key question to be sorted out, a possible return scheme between Greece and Turkey should comply with EU laws, urged Tusk.
Hu urged on the necessity of individual assessment in Greece before a decision to return asylum seekers to Turkey.
Regarding Turkey's accession to EU, "same strict conditionality applies" said Tusk.
Tusk's press statement after his meeting with Cyprus leader was as follows:
"Last week I was mandated to prepare an agreement between Turkey and the European Union on further strengthening our cooperation in the migration crisis. I am now working on the details. This is why I am here today in Nicosia. And this is why I will continue to Ankara this evening."
"The Turkish proposal worked out together with Germany and the Netherlands still needs to be rebalanced so as to be accepted by all 28 Member States and the EU institutions. The objective is to conclude the negotiations Thursday and Friday this week but we are not there yet."
"One of the issues to be sorted out is the key question of legality. We need to ensure that any new large-scale return scheme between Greece and Turkey fully complies with EU law and our international commitments. This means that we must ensure that all get an individual assessment in Greece before a decision to return them to Turkey. And it also means that we must ensure that those in need of international protection receive appropriate protection in Turkey. Another issue to be addressed is that of possible alternative routes from Turkey to other EU countries such as Bulgaria. This also has to be factored in for the agreement to be effective."
"But our cooperation with Turkey goes much beyond migration. The current dynamics offers an opportunity to reenergise the relations between the European Union and Turkey. But let me be clear in this respect. The European Union is a Union of 28 Member States. Cyprus is as important as Germany, France, the Netherlands or any other Member State. No third country can ever be more important to me than any of our Member States. We should use this opportunity, and make sure that all benefit from this new dynamics, also Cyprus."
"When it comes to accession, I want to make it clear that the rules have not changed. The same strict conditionality applies and moving forward will still require the agreement of all 28."