"That is the only way, stick together," said the Dutch manager, who is under intense pressure after one of the club's worst starts to a season in decades. "But you have to be disciplined and you have to do it together, everyone has to take responsibility, be accountable and co-operate."
Eddie Howe's Magpies avenged last season's loss to Manchester United in the League Cup final with a 3-0 victory. They played with more urgency and made Ten Hag's side look discombobulated and disinterested, and the reeling Old Trafford crowd booed the home team off the pitch at the final whistle.
"You get confidence when you get the right results, and it's only possible when you are following the rules, following the principles, be in the game, winning your battles, coming through the fight, but especially do it together, you have to do it as a team," Ten Hag stressed.
Manchester United have lost five of their first 10 home games in all competitions for the first time since 1930-31. They are eighth in the Premier League after losing five of their first 10 Premier League games for the first time ever.
Asked whether Manchester United's players have the necessary character to get through this rough stretch, Ten Hag said: "I am confident that players will stand up and stick together. This is not good enough. I am responsible for this. We have to stand up together."
Wednesday's lacklustre performance came on the heels of a similarly ugly showing on Sunday, when Manchester City throttled them 3-0 in the derby at Old Trafford.
"It's not up to the manager to motivate the players, you've got to motivate yourself," former Man United captain Roy Keane said on Sky Sports. "You've got to be up for every game, and the fact (Ten Hag) has got to discuss it after the game about his players not being up for a game of football, he must be hugely embarrassed.
"Even the point that we're talking about Man United trying to finish fourth tells you how the standards have dropped at Man United over the last few years, both on and off the pitch," he added.
Ten Hag said United needed to immediately up their game.
"We have to recover from it," he said. "We have to do it quickly. Saturday (versus Fulham) is the next game. We have to raise our standards. This is not good enough.
"We have a night sleep and then we will pick the team and the tactics. Most importantly, the mentality is where we have to prepare."
