Rival Formula 1 team bosses have questioned Mercedes chief Toto Wolff's suggestion that third cars could solve the problem of finding seats for junior drivers.
Wolff is struggling to find homes for Mercedes juniors Esteban Ocon and George Russell in 2019 as teams are reluctant to hire drivers who are tied to their competition.
During the Italian Grand Prix weekend Wolff proposed a third works entry for a rookie driver as a cheaper solution than backing a two-car "junior team," as Red Bull does with Toro Rosso.
Third cars have been discussed many times before, particularly in the context of the grid shrinking if more than one team closed down.
"It's an interesting one," Red Bull team boss Christian Horner told Motorsport.com. "But the practicalities of running three-car teams – there's things like pitstops – it's a very complicated thing to do.
"Interesting on concept, but once you get into the practicalities of it, it's very, very complex. I can't see the midfield being particularly happy with it."
The major concern of teams outside the big three is that would potentially find themselves fighting for 10th place, rather than seventh.
Williams deputy team principal Claire Williams confirmed that she would oppose any move to a third entry.
"We wouldn't be in favour of three cars," she told Motorsport.com. "You've got team collaborations and then you're going to have three cars. Where does this end? It's another step in the wrong direction."
McLaren boss Zak Brown – who could potentially have employed two experienced drivers and kept rookie Lando Norris in 2019 – indicated that he didn't object to the concept.
However, he acknowledged that it would be hard to implement.
"I like the idea of third cars, but how do you manage that?," he told Motorsport.com. "I think there's room on the grid, but not for everyone to have one. Maybe you have them at certain races, but it's got to be equal and fair."
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