Jean-Claude Juncker has told the British PM that the withdrawal agreement is "the best and only possible agreement", the EU spokeswoman stated.
According to the EU official, Juncker has promised to analyse any ideas put forward by London, "providing they are compatible with the withdrawal agreement".
The two politicians have had a phone conversation discussing the prospects of reaching a formal departure of the UK from the EU.
Boris Johnson has declared that he would like to renegotiate the "divorce" deal that both sides agreed on under Prime Minister Theresa May.
EU leaders have firmly declined to consider the possibility and stated that they only want to discuss changing an "additional political text outlining future arrangements".
Earlier in the day, UK Prime Minister Boris Johnson said that London can only agree to a withdrawal deal without a backstop, explaining that other solutions exist for the Irish border and expressing hope that the EU would rethink "their current refusal to make any changes to the withdrawal agreement". Johnson has also emphasised that the country would have to "turbocharge" its preparations for a no-deal Brexit, which would include not only mitigating the consequences but embracing opportunities.
The European Union has given the United Kingdom until 31 October to leave the bloc, with Johnson promising to deliver Brexit by that date with "no ifs or buts".