Romain Grosjean says it will not be "ideal" if Haas appoints a regular Friday practice driver in 2020.
Both Robert Kubica and Haas boss Gunther Steiner have admitted they may team up next year with a simulator and potentially Friday morning practice role for the Pole.
It would mean regular race drivers Grosjean and Kevin Magnussen would have to sit out some practice sessions.
"It is never ideal to not drive on Friday mornings," Grosjean told Ekstra Bladet newspaper.
"It also depends on what you want to achieve. You don’t see Ferrari, Mercedes or Red Bull drivers giving up Friday mornings.
"Every session is important."
As for the prospect of sitting out some Fridays next year to make way for Kubica, Grosjean added: "What will be will be, but based on performance it is never ideal."