The club announced on Sunday that a transfer had been agreed with Ajax for the 24-year-old Argentina defender.
Martinez will be reunited with his former boss from the Eredivisie soon, with the move still being subject to a medical, player terms being finalised, and to UK visa requirements.
“He’s a warrior and I think the fans will admire him. He has an attitude, fighting spirit,” Ten Hag told us.
“He brings aggressiveness in the game, in a good way. I think we need that.
“But also, he’s also skilful and he can deal with the ball and he’s left-footed.