The Prime Minister of Malta Joseph Muscat, whose country holds the rotating European Council presidency, said Britain will always be the “junior” partner in trade deals after Brexit, as it can’t match up to the power of the EU.
He said he wanted a "fair deal" for the UK after Brexit, but said that it must be "inferior" to full EU membership.
He said: "I do believe the UK is in a very delicate situation, right now. It is fetching a free trade deal with Europe and eventually the United States.
Prime Minster Theresa May (L) speaking to French President Francois Hollande
"In both trade deals it will be the junior partner because the UK is much larger than most European states, but it is smaller than Europe as a whole and smaller than the United States as a whole.
"I think it is a balancing job the Prime Minister must make. I will not judge her on the choices she makes.
"But it is pretty clear she needs to choose her priorities well."
Joseph Muscat (R) with Erica Solberg (L) at a press conference
He added: "I am one who argues there should be a fair deal for the UK and that fair deal should be achieved in the shortest time frame possible.
"But that fair deal has to be inferior to membership."
EU leaders are meeting in Valetta, Malta, today, with the Prime Minister set to say she wants a “new, positive and constructive” relationship with the EU after Brexit, according to Downing Street.
President of the European Commission Jean-Claude Juncker arrives in Malta
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Prime Minister Theresa May and UK ambassador to the EU, Sir Tim Barrow (R)
In both trade deals it will be the junior partner because the UK is much larger than most European states, but it is smaller than Europe as a whole and smaller than the United States as a whole
Prime Minister of Malta Joseph Muscat
She is also expected to underline that it is in the interests of the UK to have a strong EU.
But Mr Muscat indicated the EU had not yet decided whether or not to open future trade negotiations with the UK alongside exit talks once Article 50 of the Lisbon Treaty had been triggered next month.
The Malta leader also expressed his distain for US President Donald Trump’s temporary ban on allowing people from certain countries into America.
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Continued cooperation with the EU to tackle terrorism and international crime.
The EU flag flying in front of Big Ben
He stated: "In case of the banning people from several countries it is heavy handed and I disagree with that.
"In my books the biggest concern is the unpredictability of it all, and in an uncertain world we need to be able to predict the actions of friends."
Donald Tusk, the European Council President, also attacked Mr Trump earlier this week saying that the new US administration put the EU in a “difficult situation”.
German Chancellor Angela Merkel (R) and Lithuanian President Dalia Grybauskaite
The UK leader is also due to urge the EU Nato members to increase its spending on defence.
Britain is one of the few alliance members to meet its pledges of spending a minimum of two percent of gross domestic product (GDP) on defence.
Nato has estimated that only five alliance members – the US, UK, Greece, Poland and Estonia – will meet the target for 2016.
Donald Tusk arrives in Malta for the EU summit
Mrs May will only attend part of the EU Presidency summit in Malta’s capital Valletta and is due to leave after series of one-to-one meetings.
She is not due to be present when the other heads discuss Brexit.