The wider Red Bull GmbH company has launched a probe into Horner and he has faced lengthy questioning by an independent barrister who was appointed to draw evidence of the unspecified allegations.
Horner acknowledged at the launch of the RB20 that the matter had been a "distraction" when lightly addressing the story, for which the media had been told not to probe too far.
On the second day of pre-season testing in Bahrain, the Red Bull F1 team principal then faced his first official F1 press conference, which was streamed live to remote media while on-site journalists were not briefed on what questions would be permitted beforehand.
After initially addressing the RB20's early form, with Max Verstappen topping the first day of testing by 1.140 seconds, a question was put to Horner regarding the relationship between the main Red Bull team and its sister RB squad.
This comes amid concerns from rivals, led most notably by McLaren team boss Zak Brown, about one overarching party being able to own two teams competing in the same league and the possible advantages this may offer in terms of efficient operating under a cost cap. Horner spoke for three minutes and 37 seconds on the issue.
He was then asked directly about the investigation: "For Christian, you said it was business as usual at Red Bull. But it's not business as usual when the CEO is accused of inappropriate behaviour. So how can people take this investigation seriously when you've not been asked to step aside while it's in process?"
Source: Autosport