The Dutchman was informed of his dismissal on Monday and he leaves Old Trafford after two and a half years in charge.
Manchester United has sacked manager Erik ten Hag, the Premier League club said, with the Old Trafford side 14th in the standings after nine games.
“Erik ten Hag has left his role as Manchester United men’s first-team manager,” the club said in a statement on Monday.
“Ruud van Nistelrooy will take charge of the team as interim head coach, supported by the current coaching team, whilst a permanent head coach is recruited.”
The 54-year-old Dutchman’s job was the subject of speculation for most of last season as United recorded their worst Premier League finish in eighth, with British billionaire and INEOS chairman Jim Ratcliffe taking charge of football operations.
A surprise FA Cup final win over Manchester City, however, plus the fact ten Hag was able to blame numerous injuries for their poor form earned him another chance.
He signed a new contract to extend his stay until 2026 and get another chance to restore the 20-time English league champions to former glories.
Early results this season, however, suggested ten Hag was not going to achieve that.