Roy Keane has quit his role as Aston Villa's assistant manager with immediate effect, the club have announced.
The 43-year-old had been splitting his time between Villa and his job as Martin O'Neill's number two with the Republic of Ireland.
But Keane has stepped down from the Barclays Premier League club ahead of their trip to Burnley on Saturday.
The former Manchester United midfielder joined Villa in July to assist boss Paul Lambert after his previous backroom staff were sacked following an internal club investigation.
Number two Ian Culverhouse and head of football operations Gary Karsa left at the end of last season after an inquiry into off-field matters.
Keane said in a statement: "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.
"I'd like to thank Paul for giving me a great opportunity to come to a brilliant football club, I've really enjoyed my experiences at Villa and I wish the management team, the players, the supporters and the club nothing but the best going forward."
Lambert added: "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.
"In the brief period we have worked together he has been great in the role and I understand his reasons for leaving."
Villa, who are winless in their last eight league games and just two points above the relegation zone, will look to replace Keane as soon as possible.
Chief executive Tom Fox said: "We thank Roy for his time at the club and we wish him the best with Ireland.
"Our focus now will be on working with Paul to identify the right person to work alongside him and to help us continue on our journey to return the club to its rightful place in the Premier League."