Aston Villa rocked ahead of Burnley game as Roy Keane leaves
In what by many will be a sudden move, Keane has relinquished the role after struggling to combine it with a similar position he holds with the Republic of Ireland as Martin O'Neill's assistant.
The 43-year-old only became Paul Lambert's number two at Villa in July.
"Ultimately, my roles with Villa and Ireland and combining my commitment to these have become too much. It isn't fair to either Villa or Ireland, so I've made this decision," Keane said.
The former Manchester United midfielder, who has also managed Sunderland and Ipswich, had also been struggling to find enough time to spend with his family, a club spokesman said.
Villa manager Paul Lambert said the club would aim to fill the position as soon as was practically possible.
"Roy came to me this morning and he informed me that, ultimately, the difficulty of combining both roles has prompted his decision, which I respect totally," he said.
"In the brief period we have worked together he has been great in the role and I understand his reasons for leaving."
Villa sit just two points above the relegation zone having not won in nine league games.
They were also knocked out of the Capital One Cup by League One strugglers Leyton Orient in August.
That said they performed better against Southampton on Monday and they have faced a run of fixtures against all the top sides.