“My point of departure will be the squad of 26 players who played in the World Cup, and Cristiano Ronaldo is one of them,” Martinez told a press conference.
Martinez added that he would make his decisions “on the pitch and not in an office”.
Martinez, who cut his managerial teeth at Swansea City, Wigan Athletic and Everton, took over as Belgium coach in 2016, leading the side to the 2018 World Cup semi-finals.
Under his leadership, Belgium were top of the FIFA world rankings for more than three years.
But his time with the Red Devils came unstuck in Qatar, where they overcame Canada 1-0, but were then beaten 2-0 by Morocco before a goaless draw with Croatia ensured an early departure.
Portugal had Santos at the helm for eight years and the 68-year-old led the team to their first ever international titles: the 2016 European Championship and the inaugural 2019 Nations League.
Santos quit as coach five days after Portugal exited the World Cup at the quarter-final stage.