Christian Horner enquiry could drag on after initial Red Bull hearing
Red Bull Racing and the Austrian energy drink parent company, who have not detailed the nature of the complaint, remained tight-lipped with representatives not responding to calls or emails.
F1 insiders told Reuters they understood the hearing was held in London at an undisclosed location rather than the team's Milton Keynes factory.
Sky Sports television reported the meeting with an independent barrister lasted almost eight hours.
One informed source told Reuters that Briton Horner denied the allegations 'in the strongest possible terms' at a meeting this week of the Formula 1 Commission.
Sources cautioned there might not be any outcome until after the scheduled car launch next Thursday, with the barrister possibly needing to carry out further hearings.
Former F1 supremo Bernie Ecclestone told Reuters he spoke to Horner on Thursday evening.
The pair have been close for years and Horner, who is married to former Spice Girls singer Geri Halliwell, was best man at Ecclestone's wedding to Brazilian third wife Fabiana Flosi in 2012.
Ecclestone was also close to Red Bull's late co-owner Dietrich Mateschitz.
"I spoke to him yesterday and it was the normal Bernie and Christian conversation about things in general," he said. "We had a chat about what's going on in the sport."
Investigation launched
Red Bull Austria said in a statement on Monday that they were investigating a complaint against Horner, without saying where it came from or what it was about.
"After being made aware of certain recent allegations, the company launched an independent investigation," it said.
"This process, which is already underway, is being carried out by an external specialist barrister. The company takes these matters extremely seriously and the investigation will be completed as soon as practically possible."
The BBC and Sky Sports television said they understood the complaint related to inappropriate behaviour of a controlling nature towards a female member of staff.
Red Bull are due to launch their 2024 car at the Milton Keynes factory, an event that will also celebrate the team's 20th season.
Horner, the man who has guided them to six constructors' titles and seven drivers' championship in that period, would be expected to attend along with triple world champion Max Verstappen, teammate Sergio Perez and other senior figures.
Horner and his team celebrated the most dominant season in Formula 1 history last year, with Red Bull winning 21 of 22 races.
The Briton is the longest-serving team boss in Formula One and was by far the youngest when he led Red Bull into the sport in 2005.
Should Horner have to stand down, the effect on the sport would be seismic.
Such a shock could also lead to the departure of other key team members, with rivals Ferrari known to have tried to lure away star designer Adrian Newey in the past.
