Martinez told Clank Media: "The club is obviously going through a process of change. Since Six Alex Ferguson's departure, they haven't found a manager who hits the right note. Ten Hag did a remarkable job at Ajax, which is why he went to United, and thanks to him, I joined the club as well.
"It's like everything in life: you take a gamble, and sometimes it works out well, sometimes it doesn't. I think that, like any club, if something isn't working, it needs to be changed. It's necessary to analyse what's working and what isn't and make changes accordingly because that's how great clubs operate. Manchester is one of the best clubs in the world.
"Now Ruben Amorim has arrived with very good energy and willingness. I believe he will make the necessary changes. Without a doubt change is needed, because where we ended up in the table over the last two seasons is unacceptable."