Fernando Alonso calls in sick ahead of 400th F1 race weekend
The team said the Spaniard, who had been due to take part in a news conference at Mexico City's Autodromo Hermanos Rodriguez, was feeling unwell and would skip his regular media activities.
"Fernando is focused on feeling 100% for Friday and his planned return to the AMR24 (car) for free practice two," the team said.
Brazilian reserve Felipe Drugovich had always been due to take Alonso's place in first practice.
Although Sunday will be Alonso's 400th race weekend, he has actually started 'only' 396 races so far.
He was unable to re-start Belgium 2001 with Minardi, missed the infamous six-car 2005 U.S. race with Renault and was out of the 2017 Russian Grand Prix before the start due to a McLaren engine issue.
Alonso, who debuted with Minardi in 2001 and won his titles with Renault in 2005 and 2006, has still taken part in more than a third of all World Championship Grand Prix held since the first in 1950.
Winner of 32, his last victory was in Spain with Ferrari in 2013.
"Championships and race wins are what matter most to us as drivers but, at the same time, it shows my love for the sport and the discipline I've had to perform at a very high level for more than 20 years," he said in a team Q&A.
"I don't think I'll be adding another 400 to my total, but hopefully I've got at least another 40 or 50 more races to come in the next couple of years."
The oldest current driver, Alonso stands out in Formula One also as a driver who has had success in other series.
A two-time winner of the 24 Hours of Le Mans with Toyota, he is a world endurance champion and in 2017 led the Indianapolis 500 for 27 laps before his car's engine failed. In 2020 he finished 13th in the Dakar Rally.
"I think modern F1 is easier on the body than previous eras and that allows you to compete for longer," he said.
"It's still a huge physical challenge, but the technology in F1 has changed so the cars are a little friendlier to the drivers. Seat comfort, safety equipment, helmets -- everything has evolved into a better place."