Tusk told journalists in Brussels on Wednesday afternoon that a deal was within sight, as London and Brussels intensify negotiations that center on solving the Northern Irish border issue.
"The basic foundations of an agreement are ready and theoretically tomorrow we could accept this deal with Great Britain," Tusk said via a live broadcast on Poland's TVN24 news channel.
Earlier in the day, Tusk had reportedly claimed that "theoretically, in seven or eight hours everything should be clear" - implying that Brexit negotiations had arrived at a highly significant juncture.
The growing positive soundings from UK and EU officials around prospects of a Brexit deal finally being agreed in time for the crucial European Council Summit on Thursday and Friday has been somewhat tempered by key Brexit players in the UK.
Talk of an agreement including a customs border in the Irish Sea, ostensibly meaning Northern Ireland would be treated differently to the rest of the UK, has antagonized the Democratic Unionist Party (DUP), PM Boris Johnson’s allies in government.
A spokesperson for the UK prime minister reported that Johnson said“we are not there yet” on an agreement and that negotiations are still ongoing with the DUP.
It comes after UK Brexit Secretary Stephen Barclay revealed to a select committee of MPs on Wednesday morning that the government had sent the all-important critical documents outlining the future relationship to EU officials.
“Everything is going in the right direction, but you will have noticed yourselves that with Brexit and above all with our British partners anything is possible," Tusk said, adding that there were still "certain doubts" on the UK side.
Johnson has until Saturday to finalize a deal with Brussels, otherwise UK law states he must request a delay past the October 31 Brexit deadline.