Sir Keir Starmer is weighing up his political future as pressure grows on him to announce his resignation.
It comes as cabinet ally Peter Kyle said the prime minister was considering "political realities" after Andy Burnham's victory in the Makerfield by-election last week cleared a path for him to challenge for the Labour leadership.
In the wake of the result, the prime minister has faced fresh pleas from senior ministers to effectively make way for Burnham by setting out a timetable for his departure.
And in a further blow to the embattled Labour leader, US President Donald Trump said Sir Keir "will resign as prime minister", as he attacked his record in office.
In a social media post, Trump said Sir Keir had "failed badly" on immigration and energy policy, as he repeated his calls to "open North Sea oil".
He added: "I wish him well!"
No 10 told the BBC the two leaders, who last saw each other at a G7 summit in France last week, had not spoken over the weekend.
In the immediate aftermath of Burnham's victory, Sir Keir continued to insist he would fight any formal leadership bid, meaning a contest in which Labour members and affiliated trade union supporters decide on the party's future would be needed.