The Red Devils were held to a 1-1 draw in the Europa League group stages against FC Twente.
Despite going into the game as huge favorites and taking a 1-0 lead, United could not get the job done.
Post-game, Ten Hag told reporters about facing his old club: "In this moment, with my team, we want to improve and we want to make a successful season so there is no place for sentiments like this.
“It was a special match because I have a history there (at FC Twente) but you have to turn it off, don’t think about these things, you have to not be in the emotion and you have to clinical and prepare the team you are working for and is now also in my heart. That’s what I did with all my heart and in my head."
On United, he added: "We have to build and tomorrow we have to keep going. Tonight was not good enough; we should have won. We kept the opponent alive and we did not finish it off after we went 1-0 up, that’s not good, we know this and we have to learn from this. We have to be more secure, we have to look for more moments where we can dominate the ball and speed up the game to go for the second goal."
On Rasmus Hojlund being back, he finished: "Of course, they (the forwards) are all main (forwards), but Joshua (Zirkzee) is doing very good. He created a very good chance, it was a brilliant shot and a very good stop. We are very pleased that Rasmus (Hojlund) is back, of course, and now he has to come up to full fitness, full speed, and he can score a goal, we know that. He’s very good in the box."