The post of shadow Scottish secretary remained vacant as Jeremy Corbyn vowed to fight on in spite of an overwhelming vote of no confidence by his MPs.
Mr Corbyn said he would not “betray” supporters by resigning, underlining the mandate he won in last year’s Labour leadership election.
He added the vote by the parliamentary Labour party had no “constitutional legitimacy” under the rules.
The motion of no confidence was supported by 172, with just 40 backing the Islington MP and four spoiling their ballot papers.
As the news emerged, Scottish Labour Leader Kezia Dugdale said she would quit in the same circumstances.
The MSP stopped short of calling for Mr Corbyn to resign, but added: “If I was in his position, if I had lost the confidence of 80% of colleagues I would resign because I could simply not do my job.”
Meanwhile, sources suggested the leadership could try to reappoint Ian Murray, Labour’s only MP in Scotland, who stepped down over the weekend.
SNP Westminster Leader Angus Robertson has written to Mr Corbyn urging him to get someone in post urgently.
The Moray MP added: “While the SNP continues to provide effective opposition and strong leadership, the Scottish people also deserve to have scrutiny of the UK government by the official opposition.
“Scotland deserves better at this crucial time.”
In a statement after the vote, Mr Corbyn said: “I was democratically elected leader of our party for a new kind of politics by 60% of Labour members and supporters, and I will not betray them by resigning.
“Our people need Labour party members, trade unionists and MPs to unite behind my leadership at a critical time for our country.”
His determination to continue in the top job means MPs will have to mount a formal challenge if they want to oust him.
Among those who could run are Angela Eagle, who quit the shadow business brief this week, and Tom Watson, the party’s deputy leader.
But Mr Corbyn’s allies are confident he would win again in a ballot of grassroots activists and his team insist he would automatically be a contender as the current incumbent.
Any Labour MP wanting to challenge Mr Corbyn would require the support of at least 20% of their parliamentary colleagues, which at current levels – with 229 MPs – equates to about 50 signatures.