Jose Mourinho has accused Manchester City of a lack of class after the airing of their behind-the-scenes documentary 'All or Nothing'.
A film crew followed Pep Guardiola's side as they won the Premier League title with a record points tally in the 2017/18 season.
The eight-part series was released on Friday, showing clips from inside the dressing room, the boardroom and on the training ground.
But Manchester United manager Mourinho was not impressed.
He told Sky Sports: "You can have a fantastic movie while respecting others.
After finishing second last season, United will be looking to topple City this year.
But Mourinho is expecting a tough campaign, especially as several top-six rivals have strengthened over the summer.
"Last season we put ourselves in a difficult position, because to do better we can only finish first," said Mourinho.
"Liverpool are trying to win the title with their amazing investment. Chelsea have a fantastic squad, Manchester City have a fantastic squad too, Tottenham made an incredible investment by keeping their players, that's the best investment you can make. They could be spending £200m but if they lose Harry Kane or Christian Eriksen...the biggest investment was keeping all their best players. Arsenal will be better even though they lost their first match.
"I think it's going to be a very hard season."