Polesitter Will Power will miss the warm-up for today's St Petersburg race due to illness, and is in doubt for the IndyCar season opener itself.
The Team Penske driver has a stomach virus that will force him to sit out Sunday morning's warm-up session, with IndyCar veteran Oriol Servia called in as cover.
The Spaniard will drive Power's #12 entry in the warm-up and is on standby for the race.
Power was not slowed by the virus on Saturday, setting a new track record, 1m00.2450s, to claim his sixth pole in seven St Petersburg events.
"Unfortunately, I've been feeling pretty ill all day," he said on Saturday evening.
"It was a struggle to get through qualifying, honestly, but we were able to do it and after the pole award presentation I just started feeling a lot worse.
"I'll try to get some good rest tonight and come back ready to race on Sunday."
A decision on Power's condition will be made closer to the race.
If Power is unable to take the start, Servia will make his 198th start across CART and IndyCar.
His last appearance was the 2015 season finale at Sonoma, driving for Andretti Autosport following Justin Wilson's death.
UPDATE: Servia finished with the ninth-fastest time in the warm-up session, second of the four Penske drivers in the order and 0.7408 seconds off pacesetter Takuma Sato.
Autosport Race Centre Live will bring you full coverage of the season opener from 4:45pm UK time on Sunday.