The Dragoes have captured the 25-year-old target-man, amid rumours that Hulk is set to leave the club over the summer
The 25-year-old has signed a four-year contract with the Portuguese champions, with a minimum release clause of €40m, and will be presented to the fans, over the weekend, after passing the mandatory medical checks.
The centre-forward has played 64 league games for the Mexican side, scoring 33 goals in just two seasons with the Chiapas outfit.
The former Independiente Medellin hitman has also represented his country 14 times, bagging five goals, his last in a 2-0 friendly win over Jamaica in September 2011.
The signing of Martinez will only add to the speculation that Hulk is to leave the club over the summer, with the Brazilian international being linked heavily with Chelsea.