Manchester United manager Jose Mourinho blamed "individual and collective mistakes" after his side suffered a third successive defeat.
United's 3-1 loss at Watford on Sunday followed defeat against Manchester City in the Premier League and Feyenoord in the Europa League.
With the game goalless, Anthony Martial lost possession leading to Etienne Capoue scoring the opening goal and Mourinho felt a foul should have been given for Miguel Britos' challenge. Although Marcus Rashford eventually equalised, Watford went on to win through a goal from substitute Camilo Zuniga and then a Troy Deeney penalty.
Mourinho told BT Sport: "There's no debate, no controversy.