Assistant manager Roy Keane has left Aston Villa with immediate effect, the club have announced.
The Ireland assistant manager joined the Premier League outfit earlier this year, but, after a good start, Villa have endured a torrid time.
Press Association is reporting that the former Manchester United captain has quit the club.
'Ultimately, my roles with Villa and Ireland and combining my commitment to these have become too much,' he said.
"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."
Paul 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."
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.
Aston Villa are due to play Burnley tomorrow.
Keane joined up with Lambert in July after snubbing an approach from Celtic for the vacant managerial role at Parkhead.
At the time Keane said he would have no problem combining both the Villa and Ireland roles.
He said at the time: "I am looking forward to linking up with Paul Lambert at Aston Villa and thank Martin and the FAI for giving me the opportunity to do so.
"I remain totally committed to my job with the Republic of Ireland and all that it involves.
"This agreement promises to be an exciting challenge and will give me an opportunity to continue developing my coaching skills on a daily basis that should ultimately benefit everyone."
CEO Tom Fox added: “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.”