During a question and answer session with young YouTube users, Juncker also denied that he was threatening Britain when he said in a flagship speech this week that it would "regret" Brexit.
His comments came as a senior European Commissioner separately rejected suggestions that Britain would be at the back of the queue when it came to a future trade deal.
"My working hypothesis is that there will be a deal," Juncker said.
"I don't want to imagine a situation where Britain will leave like that, saying goodbye without there being an arrangement for the future. I don't envisage what people call a 'hard Brexit'."
Britain and the EU are currently in negotiations on its departure from the bloc on March 29, 2019, following its shock referendum decision to leave last year.
But the EU has refused to discuss a trade pact until there has been progress on the terms of the divorce -- including the bill it says Britain must pay -- raising concerns about whether there will be enough time to reach a deal by Brexit Day.
Without a deal Britain faces a "hard Brexit" with trade tariffs and a range of other problems including immigration and travel difficulties.
Former Luxembourg premier Juncker said in his annual State of the Union speech on Wednesday that "we will regret it (Brexit), but you will regret it too".
"I don't want to punish, sanction or make Britain suffer", Juncker said, adding that "I like the English too much".
Juncker's speech put a priority on striking trade deals with Australia and New Zealand before his mandate ends in 2019, but Jyrki Katainen, the European Commission vice- president who oversees investment issues, said this did not mean a British deal was not also important.
"I've read (news)papers which sometimes refer to some of us saying the UK is the last possible partner with whom we want to negotiate trade. Forget this nonsense," Katainen told a news conference.
"As soon as we know when we can start negotiating about the future arrangement, (trade) negotiations will start then. From our side there is no political priority that we want to keep the UK last in the row," he said.
EU trade commissioner Cecilia Malmstroem added: "Keep calm, don't panic.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)