Christian Horner, the head of Red Bull, the reigning world champions of Formula 1, attended a hearing on Friday to respond to allegations regarding his conduct, raising questions about his future and potentially overshadowing the unveiling of the team's new car next week. The Red Bull Racing team and the Austrian energy drink company have remained silent regarding the nature of the complaint and their representatives did not respond to calls or emails. Sources told Reuters that the hearing took place at an undisclosed location in London, not at the team's factory in Milton Keynes.