At last month's European Union summit in Salzburg, Mr Tusk rejected Theresa May's Brexit proposals and sparked anger among some Tories with an Instagram post apparently poking fun at the prime minister and suggesting she was "cherry picking".
She added: "We asserted our common position that the "backstop" as already agreed must be maintained and is the absolute bottom line for Sinn Fein, SDLP, Alliance and Green Party".
Tusk said that now that the Conservative Party conference had ended, "we should get down to business".
But Tusk said he wouldn't change his approach to negotiations, saying: "Telling the truth, even if hard and unpleasant, is the best way of showing respect for partners". The EU is about freedom and human rights, prosperity and peace.
British Foreign Secretary Jeremy Hunt said over the weekend that the EU shouldn't try to prevent a smooth Brexit because "it was the Soviet Union that stopped people leaving".
Mr Juncker told reporters in Austria that the current holder of the rolling presidency of the European council that recent days had provided some cause for optimism in the talks.
Boris Johnson and other hard Brexit Tories seized on Tusk's remarks, arguing they showed it was time for May to immediately switch tack and abandon her Chequers proposals for remaining in a customs union for food and goods.More news: Conor McGregor Claims Khabib's Manager Is A Terrorist
"I believe that we must distance ourselves from this no deal scenario", the former Luxembourg prime minister said.
Mr Tusk and Mr Barnier have said the next European Union summit on October 18-19 will be the "moment of truth" when it should be become clear whether it is possible for the two sides to reach an agreement.
Leo Varadkar is not sure what final form a "Canada-style" deal would take.
EU Brexit negotiators told ambassadors of the 27 states remaining in the bloc on Friday that there was no breakthrough on the Irish issue and much would depend on what the British bring to Brussels next week.
'My assumption is that we will reach an accord which will achieve the conditions of the withdrawal treaty, ' Juncker said, adding that it was not possible to predict whether there will be a conclusion to the Brexit negotiations in October.
Mr Tusk also rejected any suggestion that the EU had not respected the dignity of the United Kingdom at the recent meeting of European leaders at Salzburg.
The two sides are hoping to make progress on the thorny issue of the Irish border in time for a summit on October 17 and then seal the agreement a month later.