Medel, who plays with Welsh club Cardiff, played as a defensive midfielder in his club's unsuccessful bid to survive in the Premier League last season but plays at the back for his country.

Now, as Jorge Sampaoli's men seek to inflict more pain on defending champions Spain after their opening humiliation at the hands of Holland, Medel says he wants to play a pivotal role to see off La Furia Roja.

Medel turned in a strong shift in the 3-1 win over Australia to get the Chileans off to a flyer and thinks the South Americans have built a strong platform.

He says he and his compatriots will roll their sleeves up and do all they can to push the Spaniards towards the exit.

"The pitbull only bites when he has to," Medel told reporters, but admitted he is itching to start at the mythical Maracana.

"I feel very important in this team. I can speak firmly with my teammates and shout more in the dressing room," Medel reflected, confident in his linchpin status at this his second World Cup.

Standing just 1.72m (5ft 9in) Medel is a stabilizing influence on a side which has its sights on a place in the last 16.

- Sharpening his teeth -

With his stocky stature and tough tackling style Medel gained his Pitbull monicker while with Universidad Catolica back in his homeland.

Thereafter, he spent three years in the hothouse of the Argentinian league with Boca Juniors.

He then joined Sevilla prior to his move to Cardiff a year ago.

After a spate of red cards in his earlier days Medel has matured and now is a mainstay of the Chilean squad.

Compared to the likes of Germany, Chile conspicuously lack height -- their average is just 1.75m. Spain's average is 1.79m while remaining rivals Holland boat an average of 1.84m.

Marcos Gonzalez does lend height, however, at 1.91m.

Australia did pose a threat on occasion -- Tim Cahill pulling a goal back and having another chalked off.

Sampaoli has therefore been drilling the side to cope better with aerial threats -- knowing that even after their Spanish test, flying Dutch maestro Robin Van Persie will be lurking in the final group game.