Donald Franciszek Tusk is a Polish politician who has been the President of the European Council since 2014. He served as Prime Minister of Poland from 2007 to 2014 and was a co-founder and chairman of the Civic Platform political party.
As campaigning ramps up ahead of next month's general Election , he warned that leaving the EU would leave the UK a "second-rate player".
He is due to step down from his role next month, having held The Post for five years.
Mr Tusk's intervention comes as Conservative leader Boris Johnson said the UK Parliament was "paralysed" and had refused "time and again to honour the mandate of the people and to deliver Brexit".
"I think The Principle that politicians don't comment on the electoral affairs of other countries is a wise principle," he added.
Meanwhile, the UK has continued to refuse to put forward a candidate for the next European Commission , which is due to take office next month if approved by MEPs.
However, he is understood to have insisted the UK does not want to stop The Commission being formed as soon as possible.
But Labour is promising to renegotiate that deal and put it to a referendum, with the option of remaining in the EU, if it wins the Election - and smaller opposition parties are campaigning to Remain.Brexit 'extra time'
Speaking at the College of Europe In Bruges , Mr Tusk said: "Brexit may happen at the beginning of next year.
"I did everything in my power to avoid the confrontational no-deal scenario and extend the time for reflection and a possible British change of heart".
"The UK Election takes place in one month. Can things still be turned around?
"In this match, we had added time, we are already in extra time, perhaps it will even go to penalties?"
Donald Tusk 's term of office ends in a few weeks' time.
And that he feels free to challenge the sense developing among the rest of the EU, that it would be better if the UK left as soon as possible.
His message was simply not to give up.
The EU has accepted an extension to the Brexit deadline, meaning the UK is now due to leave at the end of January 2020.
He acknowledged this in his speech, adding his remarks were "something I wouldn't have dared to say a few months ago, as I could be fired for being too frank".
Mr Tusk is due to stand down from his role on 1 December, when he will be replaced by former Belgian PM Charles Michel .