United surrendered four unanswered goals in the first half of Saturday’s game, leaving the new manager with no points in his first two games in charge.
The players were supposed to have a day off, but Ten Hag was so upset with his team’s performance that he ordered them back into training less than 24 hours after the game for an extra session, according to The Times.
Goalkeeper David de Gea, who was at fault for the first Brentford goal, has admitted that United is still dwelling on previous disappointments from seasons gone by and urged his squad to stick together.
“Of course, there have been some difficult seasons and probably, it’s still in our minds,” he told ESPN.
“When something goes wrong people get panicky. It’s difficult. But we have to learn, we have a new manager and some new players. We need to be more positive, keep learning and improve.
“It’s about winning games. As soon as we win one game, two games, we’re going to start feeling better and more positive.”