In the wake of unspecified claims that are understood to have been made against him by a female employee, parent company Red Bull in Austria has opened up an official probe into the matter.
A statement issued by it on Monday said: “After being made aware of certain recent allegations, the company launched an independent investigation.
"This process, which is already under way, 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. It would not be appropriate to comment further at this time."
It is understood that Horner will now meet with the independent legal representatives on Friday to discuss the matter.
Horner, who has continued in his team principal duties and attended the F1 Commission meeting in London on Monday, has strongly denied any wrongdoing.
Speaking to Dutch newspaper De Telegraaf, Horner said: "I completely deny these claims."
Red Bull's F1 team has not made any comment on the matter.
The situation surrounding Horner comes ahead of an important period for the Red Bull team, as it finalises its preparations for the 2024 F1 season.
It is scheduled to launch its new car, the RB20, at its Milton Keynes factory on February 15 – less than a week before the official pre-season test in Bahrain begins.
Chief technical officer Adrian Newey has revealed that the new design will be a ‘third evolution’ of the original RB18 design from 2022 which has proven to be the car best suited so far to F1’s new ground-effect regulations.
Red Bull is coming off the back of one of the most dominant seasons in F1 history, as it won 21 out of 22 races to secure both the constructors' and drivers’ world championship with Max Verstappen.
Horner has led the squad since it entered F1 in 2005 and is now grand prix racing’s longest-serving team principal.
His achievements in F1 led to him being awarded a CBE in the recent New Year's Honours list, for services to motor racing.
