Fronting the media, including Speedcafe.com, in Singapore, Horner reacted angrily to the suggestion that his team has broken the rules, suggesting it is a cynical effort to take the gloss off the possibility of Max Verstappen sealing the 2022 title this weekend.
He further suggested that Red Bull would explore its options over potentially defamatory remarks.
“We were a little bit taken aback by comments that were coming in from two of our rival teams yesterday,” Horner began.
“The [financial] submission between the team and the FIA is one that is confidential. I have no idea what the outcome of our rival submissions are, or the accounting treatment or so on.
“I would be intrigued to know where their source of information for these fictitious claims has come from.
“They're hugely defamatory,” he added.
“We take umbrage to them, and one can only assume it's not a coincidence.
“It's not uncoincidental that this is at a point where Max has his first strike [at] the World Championship.
“How on earth do they have this information? Where do they have this knowledge? The FIA have even stated they haven't even completed their process.
“So unless there is a clear withdrawal of those statements, we will be taking incredibly seriously and looking at what the options available to us are.
“It is absolutely unacceptable to be making comments of the type that were made yesterday, that is totally defamatory to the team, to the brands, and even to Formula 1.”
Teams submitted their financial results for 2021 in March.
Since then, the FIA has worked with teams over their accounts, with certification of those results expected on Wednesday.
Given that process is not yet complete, Horner took issue with the accusations levelled at his squad.
He was also on the attack when asked about specific comments naming Red Bull.
“They were very clear in naming Red Bull,” he shot back at the journalist who quizzed whether Red Bull was actually named.
“I know you have impartiality for some teams, but it should remain absolutely neutral.
“The facts are such that the submission is made to the FIA, and it is a private submission between the team and the FIA.
“So how on earth can any team know the detail of our submission? How on earth can any team know that a team is in breach or not?
“We don't even know. If we're in breach, we don't even know until next week, until the process has been completed.
“So perhaps, when these accusations are made, people in glass houses shouldn't throw stones.
“And we take umbrage, and extremely seriously the remarks that have been made,” he reiterated.
“Is it any coincidence that Max has his first shot at winning a world title? And here we are talking nothing but cost caps rather than the phenomenal performance that he has had this year.
“I think it's an underhand tactic that has been employed to detract from perhaps a lack of performance on track this year.
“So and of course, when references are made to last year, this year, next year, we're going to take that extremely seriously.
“This is an issue for the FIA to deal with but also an issue for Red Bull to consider what our position is with those comments that have been made.”
The FIA is set to hand down its findings on the team's financial submissions from 2021 on Wednesday.