Romain Grosjean says that potentially giving up Friday practice sessions next year to allow Haas to run Robert Kubica would not be "ideal".
Haas is in talks with Kubica for a testing and development role in 2020, with the US outfit believing it could benefit from including the experienced Pole in its extended line-up.
Haas relied this season on the simulator work of development drivers Pietro Fittipaldi and Louis Deletraz, but team boss Guenther Steiner said that Kubica's potential involvement next year would likely involve a series of FP1 outings.
"Giving [up] Friday morning is never ideal," Grosjean said, quoted by RaceFans.
"It depends where you want to fight and what are your ambitions. We’ve never seen Ferrari, Mercedes or Red Bull giving Fridays because I think they want to fight for the win.
"Every session is important. If it’s got to be, well be it. But I think in terms of performance, it’s never ideal."
Having to hand over your car to a test driver is something Grosjean experienced during his final year with Lotus in 2015, when hopeful Jolyon Palmer was awarded numerous FP1 outings.
"If you have a good car and the set-up is balanced, it's fairly easy to jump back in. If there's a lot of work to be done on the car it's a big setback," said the Frenchman.
Kevin Magnussen also emphasized the importance of Fridays for the team's regular drivers.
But the Dane also wondered why Haas would need to recruit Kubica given Fittipaldi's productive work in the team's simulator.
"We already have Pietro Fittipaldi and he is already doing a good job in the simulator," said Magnussen.
"He's a good team member. So I think we've got that covered already. That's not something I'm involved with, that decision.
"I don't like it when you get taken out in FP1. FP1 is valuable. It's just those extra set of tyres you get, they are valuable. I would prefer not to."
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