Hernandez is known to his fans as "El Mago", or "the magician". The Argentinean fullback come fly-half has dazzled opponents the world over with his pace, elusiveness and arsenal of kicking skills.

Hernandez made his debut for the Pumas in a 144-0 thrashing of Paraguay in 2003, but really came to prominence following his switch from Deportiva Francesca to Stade Francais. From full-back Hernandez became a force in the Top 14 and Heineken Cup, a devastating attacker joining the line and a solid defensive presence, always immaculate under the high ball. He is well remembered for a crunching, try saving tackle on Leicester's giant Samoan wing Alesana Tuilagi in the Heineken Cup clash at Welford Road in 2006.

His real arrival on the world stage was signalled by his surprise selection at outside half in the opening game of the 2007 World Cup, against hosts France. Despite being described in certain quarters at the world's best full-back, Hernandez has designs on the remainder of his career being spent in the outside half berth of both club and country.

Pumas' coach Marcello Loffereda's faith in Hernandez was rewarded by a breathtaking display of attacking skill as his side unceremoniously took the scalp of the hosts on their home turf. Hernandez continued at No. 10 for the remainder of the tournament, notching a hat trick of drop goals against Ireland in the pool decider and another against Scotland in the quarter-finals. The Argentinean effort ended in the semi-final at the hands of eventual champions South Africa, but Hernandez had impressed enough to be nominated for the IRB Player of the Year award for 2007.

A lack of opportunities in the No.10 shirt of Stade Francais led to rumours that Hernandez may be making the jump to England but these proved unfounded and Hernandez recovered from injury to rejoin Stade Francais' tilt at the Top 14 and Heineken Cup in the 2008-9 season.

In the summer of 2009 he completed a switch to the Sharks in South Africa on a one-year deal with the Durban-based side.