World champion Lewis Hamilton has hit out at Formula One's new 'Halo' concept, describing it as the 'worst looking' modification in the sport's history.
The controversial design, first pioneered by Hamilton's Mercedes team, was given its inaugural outing during winter testing in Barcelona on Thursday.
Ferrari's Kimi Raikkonen completed two laps with the halo-shaped device, which is aimed at improving driver head protection, before his team-mate Sebastian Vettel also trialled the concept on Friday.
But Hamilton, who initially told reporters he did not want to comment on the Halo, moved to clarify his position in a message posted to his Instagram account late on Thursday evening.
Alongside a picture of Raikkonen's car with the Halo attached, Hamilton wrote: "Please no! This is the worst looking mod in Formula 1 history.
"I appreciate the quest for safety but this is formula 1, and the way it is now is perfectly fine."
The FIA has explored a number of designs aimed at protecting drivers from flying debris after Felipe Massa was struck by a spring from Rubens Barrichello's Brawn during qualifying for the 2009 Hungarian Grand Prix.
Henry Surtees, the son of 1964 world champion John Surtees, was killed in the same summer that year after he was hit on the crash helmet by an errant tyre while competing in a Formula Two race at Brands Hatch.
Jules Bianchi also succumbed to the devastating injuries he sustained at the Japanese Grand Prix in July, although it is not believed improved head protection would have saved the Frenchman, while British driver Justin Wilson died last year in an IndyCar race after he was struck on the crash helmet by a piece of flying debris.
Hamilton has long been outspoken about the direction of Formula One and his social media post came just hours after he described the sport as "broken".
Asked if the sport was fundamentally broken, lacking direction or in rude health, Hamilton replied: "Probably the first two you suggested. I don't want to say too much but I agree with those."
Hamilton will be in the Mercedes on Friday morning for his final taste of testing before the season gets under way in Melbourne on March 20.