Esteban Ocon has been replaced by Ryo Hirakawa at Haas for the remainder of the Mexico City Grand Prix.
The team provided no reason for replacing Ocon, but confirmed the Frenchman was not suffering from illness.
Haas recently confirmed that Ocon will be leaving the team at the end of this season after two years with the American-owned squad, with Brazilian youngster Rafael Camara signed as his replacement.
A team statement read: "TGR Haas F1 Team reserve driver Ryō Hirakawa will replace Esteban Ocon for the remainder of the weekend's Mexico City Grand Prix, Saturday 31 October - Sunday 1 November."
Haas team principal Ayao Komatsu was questioned about the decision by Sky Sports F1 during final practice on Saturday but remained tight-lipped.
"I can't tell you much but I can tell you he's not ill," he said.
"Honestly, the only thing I can say is we are focused on what's in front of us and getting Ryo in the best shape for qualifying.
Ocon questioned the team's decision to run him on the medium rather than soft tyre during second practice on Friday.
The Frenchman pleaded "don't do this to me" to his race engineer Laura Mueller after being informed of a change to his run-plan.
Ocon had originally been set to do his race simulation on a soft tyre, but the fact his team-mate Oliver Bearman flat-spotted his soft tyres meant the team instead wanted Ocon to use a medium compound.
Hirakawa will make his F1 qualifying and race debut following nine practice session appearances, the most recent of which came when he drove in Friday's opening session in Mexico City in place of Ocon.
The 32-year-old Japanese driver's appearance in first practice was pre-planned as one of the team's obligated rookie sessions for the season.
The team statement continued: "Hirakawa, a two-time winner of the FIA World Endurance Championship (2022, 2023) and 24 Hours of Le Mans Winner (2022) with Toyota Gazoo Racing, participated in FP1 at the Autodromo Hermanos Rodriguez on Friday 30 October - his third free practice outing of the season driving the VF-26, finishing 15th overall.
"The Japanese driver will partner teammate Ollie Bearman through final practice and qualifying on Saturday and Sunday's 71-lap grand prix - Hirakawa's Formula 1 race debut."
'Ocon-Haas relationship hasn't been magnificent recently'
Sky Sports F1's David Croft:
"We don't know an awful lot. Haas are being tight-lipped. But talking behind the scenes, the relationship between Esteban and the team hasn't been magnificent in recent races. He's being replaced by Rafael Camara next season, the young Brazilian leading F2.
"He wasn't happy with the tyre allocation runs yesterday. I think you can put two and two together and make four. It's a real shame because Esteban Ocon is a fine driver."
Sky Sports F1's Jamie Chadwick:
"If you look at the tyre choice itself, in a normal situation I don't think a driver would care as much but in the situation he is in, knowing he has been dropped for next year, he is fighting for a drive.
"That is where the frustration has come from and why it has blown up into a situation we haven't seen for a long time, if ever."
Saturday October 31
5.15pm: Mexico City Grand Prix Practice Three (session starts at 6.30pm)
8pm: Mexico City Grand Prix Qualifying build-up
9pm: MEXICO CITY GRAND PRIX QUALIFYING
11pm: Ted's Qualifying Notebook
Sunday November 1
6.30pm: Grand Prix Sunday: Mexico City GP build-up
8pm: THE MEXICO CITY GRAND PRIX*
10pm: Chequered Flag: Mexico City GP reaction
11pm: Ted's Notebook
*also on Sky Sports Main Event
Formula 1 is in Mexico City where Kimi Antonelli could win the Drivers' Championship in Sunday's race at 8pm (build-up from 6.30pm), live on Sky Sports F1. Stream Sky Sports with NOW - no contract, cancel anytime
