The EU on Monday praised Turkey's efforts to meet the conditions for visa-free travel as part of Ankara's migrant deal with Brussels ahead of a decision on the issue this week.
Turkey has demanded its citizens be allowed to enter the European Union's passport-free Schengen zone without visas by June, in exchange for it taking back migrants from Europe.
The European Commission is due to to decide on Wednesday whether Turkey has met the conditions, but there are still widespread concerns among many of the EU's 28 member states.
"As you know the Commission has been working together with Turkey to ensure that the outstanding requirements of the visa liberalisation roadmap are met," Commission spokeswoman Mina Andreeva told reporters.
"Turkey has made a lot of efforts over the past weeks and days to meet the criteria, including for example extending the regulation on access to the labour market to non-Syrian refugees, and progress continued over the weekend," she added.
"Obviously the Commission will take stock of the progress in a report that will be adopted on Wednesday so I'd ask for some more patience on that."
Turkey has threatened to pull out of the migrant deal if it does not get the visa scheme.
Germany and France have proposed an emergency brake or "snap back mechanism" under which it could halt visa-free travel if large numbers of Turks stay in the EU illegally or if there are a large number of asylum applications by Turks.
The EU struck the deal with Turkey to send back all "irregular" migrants who arrive in Greece after March 20 and fail to win asylum, in a bid to halt mass migration which has created enormous strain in Europe.
In exchange the EU will resettle one Syrian refugee from camps in Turkey for every Syrian that Turkey takes from the Greek islands, the aim being to discourage people from crossing to Greece in the first place.
The accord is awash with legal and moral concerns, and critics have accused the EU of sacrificing its values and overlooking Turkey's growing crackdown on free speech in order to secure the deal.