Ferrari team principal Fred Vasseur will miss qualifying day at the Monaco Grand Prix while he remains "under observation" at a nearby hospital.
Vasseur was at the circuit on Friday when Ferrari's two cars topped both practice sessions but will miss Saturday's crucial qualifying day following medical checks.
Ferrari confirmed the news on Saturday morning but did not reveal details of Vasseur's condition.
"Fred Vasseur will not be present at the circuit today," the Ferrari statement said.
"Following some medical checks, Fred will remain under observation at a local medical facility. No further medical information will be provided.
"We wish Fred a speedy recovery and look forward to seeing him back at the track soon."
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This weekend's race in Monaco promises to be Ferrari's best chance of winning a grand prix so far this year after both cars appeared competitive in Friday practice.
Lewis Hamilton set the fastest time in the second practice session, 0.111 seconds ahead of teammate Charles Leclerc and 0.168 seconds quicker than the fastest non-Ferrari rival, Max Verstappen.
Ferrari entered the Monaco weekend with high hopes of a good result due to the nature of the tight and twisty street circuit, which plays to its car's strength and masks its straight-line speed weakness.
Qualifying for the Monaco Grand Prix, which gets underway at 4 p.m. local time on Saturday, is often a decisive session in the weekend as overtaking opportunities are so limited in the race.