|Education Secretary Alan Johnson has appealed for an end to "macho politics" in a keynote speech widely regarded as an early leadership pitch.
Mr Johnson warned that Labour risked self-destruction if the squabbling of the past week continued.
Issuing a call for unity, he warned that there must be "no resort to personal attacks" at any stage of the leadership transition process.
And he called for an "honest, measured and comradely" debate to help ensure Labour a fourth term.
Mr Johnson's comments came in a speech to the Social Market Foundation which ranged well beyond his education brief.
He has already indicated that he will stand for the deputy leadership when John Prescott stands down, and is widely tipped as a potential Blairite challenger to Gordon Brown for the leadership.
Asked on Wednesday whether he intended to run for the leadership Mr Johnson blushed and smiled but declined to answer.
His speech follows Northern Ireland Secretary Peter Hain's confirmation on Tuesday that he would stand as deputy leader.
After a week in which eight MPs quit Government jobs over Tony Blair's leadership, Mr Johnson acknowledged: "Last week was not my party's finest hour. We must ensure that the self-indulgence of what was literally macho politics does not escalate into self-destruction.
"There must be no resort to personal attacks either now or at any stage of the eventual transition process."