The 2023 FIA sporting regulations theoretically permit as many as three new teams to enter to take the grid up to 26 cars. The extended deadline for interested parties to apply for the 2025-27 seasons is 15 May.
Andretti - in conjunction with General Motors firm Cadillac - Panthera Team Asia, and Hitech GP are viewed as the more credible candidates, while the LKY SUNZ party has recently stated its interest.
But most existing teams, who can offer an opinion but will not have a say in the final decision on whether to add new competitors, do not want to diminish their share of the prize money.
Horner has now offered a new objection, arguing that some circuits added to the F1 calendar would not be able to house more cars due to the restricted pitlane and garage space.
He said: "With the way that the sport has now developed, if you look at the pitlane, for example here [in Miami] or somewhere like Monaco or Zandvoort or some of the circuits that we're now racing at, where would we be able to accommodate an 11th team?
"That in itself, just operationally, where do we put the motorhomes? Where do we put the support? Where do the trucks go?
"I just think it would be an incredibly difficult thing to be accommodated with the way that the sport has currently evolved as well."
In public, McLaren boss and historic motorsport fan Zak Brown is more open to an expanded grid, citing the 1980s and 90s pre-qualifying shootout used to whittle down grids of 30 cars.
However, he says of the parties to express interest in F1 over recent years, 2016 debutant Haas remains the only "credible, sustainable" team he has seen among a pool of "dreamers".
He said: "Really the only credible, sustainable team that I've seen in the last decade is [Haas].
"So, what we do need to make sure is if someone enters that they really have the commitment and can do what it takes.
"In my experience, in a variety of motorsports, you do see a lot of dreamers.
"What we don't need with the health of the sport is a team coming, underestimating what it's going to take and two years later they're gone.
"Hats off to Haas for the commitment they've made and continue to make to the sport. We need more teams like that."
