Martinez in his first year at Ajax played as a defensive midfielder and did really well. It was clear he was a good player.
Good tackler, agile, technically versed, positional awareness. It was really a surprise and unfair that Martinez was merely a bench player in his second year, because Ten Hag concluded that he was only suited as a defender. A quick look and you might not have noticed, but in 20/21 season he was often just a substitute or replacement for either Blind or Tagliafico.
And then this season we found a golden duo with Timber and Martinez, which drove Blind to left back and Tagliafico (Argentinian international) to the bench.
Martinez missed some games this year, but that was because of injury. Otherwise he was one of our best and most important players.
Ten Hag is not going to use him in midfield. Especially because he would also get in the way of De Jong.
You should forget about putting a pure defensive midfielder next to De Jong.
It would only limit him and Ten Hag knows that.