Ferrari team chief Fred Vasseur was absent from the Monaco Grand Prix on Saturday due to medical reasons, the team said in a statement.
Ferrari drivers, seven-time champion Lewis Hamilton and local hero Charles Leclerc, had topped the times in Friday practice and were favoured to shine in qualifying.
In a statement, Ferrari said: “Fred Vasseur will not be at the circuit today. Following some medical checks, Fred will remain under observation at a local medical facility
"No further medical information will be provided."
Ferrari added that they looked forward to "seeing him back at the track soon".