Kimi Antonelli is due back at the Autódromo Hermanos Rodríguez on Friday for opening practice, but as of this writing Mercedes has not confirmed that he is over the viral illness that kept him away from Thursday's media day.

First practice for the Mexico City Grand Prix starts at 12:30 local time (18:30 UK), and it will be the first real sign of how ready the championship leader is for his title-deciding weekend. Thursday's absence was covered in GPblog's earlier report.

Since then, Mercedes has not made any new public statement. The team's only word on his condition is still the short note it put out on Thursday, before the drivers went on track.

Mercedes still to give Antonelli the all-clear

Mercedes was clear that it expects him back, but it stopped short of saying he is fully fit. The team expects him for Friday's running but has not confirmed that he will be fully fit for practice or the race. That leaves the opening session as the first chance to see his condition for real.

Vesti already committed to Russell's car in FP1

Mercedes had already filled one seat for FP1 before Antonelli fell ill. George Russell is sitting out the session so that reserve driver Frederik Vesti can drive his W17, under the rules that make regular drivers give up their cars to rookies twice a season. So the team's reserve will already be in a car on Friday afternoon.

If Antonelli is too ill to race, the seat is likely to go to Vesti. He would make his Formula 1 race debut after six free practice sessions with the team.

Toto Wolff, meanwhile, asked for calm as Mercedes chases the titles. "The championships are moving closer, but our mindset does not change," the team principal said, adding: "Thinking about the outcome won't help us achieve it."

Antonelli's title does not depend on him driving

Antonelli comes to Mexico after a dominant win in Austin, his ninth of the season. That left him 123 points clear of Russell with only 125 still available. Reuters noted that he will be champion if either Russell or Lewis Hamilton fails to win on Sunday, even if he finishes outside the points or does not take part.

So the virus puts at risk how he wins the title, not whether he wins it. Mercedes and its 20-year-old leader will want to seal the crown from the cockpit, though, and the answer starts with FP1. FP2 follows at 16:00 local time (22:00 UK).