Martin O'Neill has resigned as manager of Aston Villa, just five days before the start of the Premier League season.
Villa said on its website Monday that O'Neill resigned "with immediate effect" but did not give a reason for the decision.
O'Neill says in the statement that "I have enjoyed my time at Aston Villa immensely. It's obviously a wrench to be leaving such a magnificent club."
The club says reserve team manager Kevin MacDonald will take over until a permanent replacement is found. Villa plays West Ham at home Saturday in its Premier League opener.
United States coach Bob Bradley has already been linked with the job after his representatives last month discussed him potentially taking the Fulham job, which went to Mark Hughes.
"I've said over and over as well that (I'm) always excited about new and different challenges," Bradley said Monday. "Certainly coaching in Europe at some point is something that I would love to do. ... People spoke to Fulham on my behalf. I did not actually speak to anyone at Fulham."
Although Villa gave no reason for the sudden departure, O'Neill has been frustrated in recent weeks by the potential sale of key players James Milner and Ashley Young — having lost midfielder Gareth Barry the previous year and not signing a similar high-profile replacement.
Villa finished sixth last season for the third year in a row, and O'Neill has been widely credited for making the club a solid contender for the European spots since replacing David O'Leary in 2006 after a year's break from the game.
"It definitely was a bit of a surprise," said Villa goalkeeper Brad Guzan, who is in the United States ahead of a friendly with Brazil. "I spoke to some of the guys on the team, and from what they said, he left training this morning and obviously made an announcement this afternoon.
"I'm not sure (why). We've got to find a way to move forward and get ready for the start of the season."