Manchester United manager Erik ten Hag says his side made 'unacceptable' mistakes in their 3-2 loss to Arsenal in the Premier League on Sunday.
United led twice at the Emirates Stadium through Marcus Rashford and Lisandro Martinez, but were pegged back by Eddie Nketiah and Bukayo Saka before a late winner from the former sealed victory for the Gunners.
Ten Hag's men were second best after half-time, but their manager was still disappointed with the nature of the defeat.
"We made mistakes with all three goals," the Dutchman said. "Normally we are better in such situations. It can't happen. We have seen today, we still have a way to go to be top level.
"The two first goals start with a corner and we make so many mistakes from the corner to the goal. It can't happen. It's a lesson we have to take.
"We will face the players with this because it can't happen. Good teams don't make such mistakes. We had moments on the break, but we have to defend much better in that situation.
"We started the game very well, scored, are leading and then make so many mistakes that are actually unacceptable. We have to learn the lesson and move on."
United also conceded late against Crystal Palace in their previous match and had to settle for a draw at Selhurst Park.
"Two games back-to-back have been really close," Ten Hag said. "It's hard to accept when you lose in the last stage of the game.
"Today we have to accept it. We are not satisfied with this performance because we can do better. You start well and you have to take benefit from that situation. It can't happen that you concede like we did.
"This is one game. Last week we did very well. We kept them away from our box better and when they were in our box, we defended better."
