Ten Hag’s final game was Sunday’s 2-1 defeat by West Ham that left the club 14th in the Premier League with just three wins from their opening nine matches.
United are also 21st of 36 teams in the Europa League table, having drawn their three opening fixtures.
Ruud van Nistelrooy, who joined the club as Ten Hag’s assistant last summer, has been named as interim manager.
The Dutchman was informed of the decision by the club’s board on Monday morning, fewer than 24 hours after the club’s defeat by West Ham at the London Stadium on Sunday afternoon.
The club triggered a one-year extension in Ten Hag’s contract following May’s FA Cup final victory over Manchester City but just three months later he has been dismissed after overseeing United’s second worst start to a Premier League campaign.
Former Ajax boss Ten Hag, 54, took charge in the summer of 2022 and led the club to third place in the Premier League in his first season.
He also guided United to their first piece of silverware in six seasons with a 2-0 win against Newcastle United in the 2023 Carabao Cup final and finished runners-up in the FA Cup final, losing 2-1 to Manchester City.
His second season in charge started poorly, with United finishing bottom of their Champions League group in the autumn but they picked up a trophy, beating Manchester City in the FA Cup final.
British billionaire Ratcliffe told BBC Sport in February the club’s problems extended far beyond the role of the manager.
“In the past 11 years, Manchester United have had a lot of coaches and nobody has been successful in that environment,” said Ratcliffe. “That says to me there is something wrong with the environment.”
But a poor start to the campaign, which has seen United win just one of their past eight matches in all competitions, has forced the board to act.
After Ratcliffe’s investment in the club was confirmed at the start of the year, Ineos took over football operations at Old Trafford and quickly began a restructure with Dan Ashworth appointed sporting director, Omar Berrada as the new chief executive and Jason Wilcox as technical director.
The manner of United’s unexpected FA Cup win last season meant Ten Hag was given the opportunity to work within a new sporting structure but neither the results nor the performances have been good enough across last season and into this one.
The club’s hierarchy wanted to have continuity at a time of significant change, but have not seen the momentum and progress they wanted and sources stress there are no excuses for the current situation.
