The Labour leader has been unable to name all three candidates in the race to become leader of the Scottish party.
Ed Miliband named two of them - but could not remember Ken Macintosh MSP, the candidate being tipped to win.
In an interview with BBC Scotland, Mr Miliband named MP Tom Harris and deputy Scottish Labour leader and MSP Johann Lamont.
Mr Macintosh later laughed off the incident, saying: "If anything, it shows that politicians are human."
The timetable for the election will be announced at Labour's Scottish conference next month.
Mr Miliband said he believed the party had three "excellent candidates standing for the post".
However, when he was asked to name them he could only remember two of the three names.
Mr Miliband told BBC Scotland's Westminster correspondent, Tim Reid: "I think we have got three great hitters, we've got three people who are determined to show that they can make a difference, that they can make a difference to the people of Scotland."
When asked if he could name the three candidates, the politician said: "There is Tom Harris, there is Johann Lamont and a third candidate who is also putting himself forward."
After being reminded that Mr Macintosh was the third candidate, Mr Miliband said: "Look, Ken Macintosh is going to be an excellent candidate."
Following the interview, Mr Miliband phoned Mr Macintosh to apologise for forgetting his name.
Father-of-six Mr Macintosh said: "I don't think anyone should read anything into it - half the time I can't even remember the names of my own kids.
"If anything, it shows that politicians are human.
"What really caught my attention about the interview is that, like me, Ed's making a strong and positive case for Scotland to remain in the UK."
The Scottish Labour Party leader election was called after incumbent Iain Gray announced after the Holyrood poll in May that he would step down in the autumn.
A new Scottish leader is expected to be in post by the end of the year.
Mr Miliband gave his BBC interview on the final day of his party's four-day UK conference in Liverpool.