The investigation is being conducted by the wider Red Bull company, not the Red Bull F1 team which Horner has been team boss of since its inception in 2005.
Red Bull said in a statement on Monday: “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.”
A spokesperson for Horner, 50, said he “rejects these claims entirely”, although the F1 team did not comment further.
Under Horner’s guidance, Red Bull has won six constructors’ championships and seven drivers’ championships, three of which have come consecutively with Max Verstappen since 2021.
Red Bull comes into the new season off the back of the most dominant season in history, which saw the team win 21 of the 22 races. F1’s new season starts with the Bahrain Grand Prix on March 2.