Van Nistelrooy will be in charge for the weekend Premier League clash with Chelsea.
“I've seen him Monday here and I’ve spoken to him yesterday before the game," Van Nistelrooy said of Ten Hag.
“Obviously, very disappointed and touched because he really cared for the club.
“I said also yesterday, in the first conversation we had for me to come back to the club with him I really felt that he cared and loved the club and wanted to bring this club forward and that's why we connected.
“That’s why he’s also hurt that he had to leave but also proud of his achievements here with the two cups and obviously the history that he’s leaving with that.”
Van Nistelrooy also revealed a word of support from his former United manager Sir Alex Ferguson, who attended the 5-2 Carabao Cup win.
"I spoke to him. He wished me luck. We spoke shortly about my situation and shortly about the team. Most of all he wished me luck. It is always great to speak to him.”
Of his own future and the prospect of working with incoming manager Ruben Amorim, Van Nistelrooy added: “I came as an assistant to help the club forward and I'm still motivated to do so in any capacity, I go back to my assistant contract that I have here for this season and next, I'm very motivated to stay here and help the club forward, that's my absolute goal.
“We will see but it's a contract situation I'm in and my desire to help the club forward.
“I can speak to you about my side of the story and after that when a new situation is occurring and when a new manager is signing and conversations take place we have to see how things develop.”