Jack Ross has been sacked as manager of League One club Sunderland.
Saturday's defeat at Lincoln City left the Black Cats sixth in the table after 11 games of the season played.
Ross took over at the Stadium of Light in May last year and led them to the finals of the EFL Trophy and League One play-offs last season, losing to Portsmouth and Charlton respectively.
Sunderland chairman Stewart Donald told the club website: "This is a decision that has been made with a heavy heart."
Some travelling fans booed the team off the field at the end of the 2-0 loss at Sincil Bank, a result which left them four points adrift of second-placed Wycombe and eight behind leaders Ipswich.
Assistant James Fowler will lead the team in Tuesday's Leasing.com Trophy game against Grimsby.
"When we arrived at the club 18 months ago, we appointed Jack because we felt that he was the right man to take Sunderland forward over a number of years," Donald added.
"Jack has worked extremely hard, and has helped us achieve stability at the club, and I sincerely thank him for his efforts. I hope and believe that he will go on to have a successful career in management."
Prior to the former Alloa and St Mirren manager's arrival in May 2018 - a month after he was named PFA Scotland Manager of the Year - Sunderland had suffered successive relegations from the Premier League to League One.
Speaking about the size of the job in August, Ross said he "did not fear the sack" despite failing to lead them to promotion last season.
And even though league results have been mixed in the current campaign, Ross guided the team to wins over Premier League clubs Burnley and Sheffield United in the Carabao Cup and they travel to fellow third-tier side Oxford United later this month for a place in the quarter-finals.
Colin White, BBC Newcastle
In the midst of rumours that the long-awaited takeover might not be happening after all, the news - and timing - of Ross' departure have taken many by surprise.
The Black Cats have only lost two of 14 matches in all competitions this season, but on the back of last season's failure to bounce straight back into the Championship, defeat at a distinctly mid-table Lincoln on Saturday seems to have been the final straw.
Pressure is always great at a sleeping giant like Sunderland, but many supporters believe this club has the squad to win promotion at a canter, and there were audible chants of "you don't know what you're doing" during the second half of the draw at Bolton last month.
That was the first sign that even a loyal away following's support had begun to waver, but it remains to be seen whether Ross' successor can provide both attractive football and a return to the second tier.