The 21-year-old Real Sociedad centre-back isn't the biggest - a shade under 6ft - but left-footed defender is tactically aware and aggressive in the tackle.
After progressing through the "B" team - and picking up 10 yellow cards and four reds in the process - Martinez was promoted to the first-team squad for the 2011-12 season.
He's since established himself as one of La Liga's brightest young talents, earning a call-up for the Spanish Olympic squad at London 2012. Last year he was linked with Arsenal and Chelsea, while Real Madrid are also reportedly interested.
Dscipline was once an issue - he was sent off again at the Olympics - but he's cleaned up his act this term - six yellows and no reds so far.
A squat stature, but strong in the air, an excellent reader of the game and a Spanish international - sounds just like another Barcelona centre-back. The next Carles Puyol?