In a dramatic press announcement just 30 minutes before the scheduled start of Sunday's NASCAR Sprint Cup race at Auto Club Speedway, Joe Gibbs Racing announced that Denny Hamlin would not be competing in the event.

"He has a sinus infection, and it's affecting his vision, so he won't be able to start the race today," said team president JD Gibbs, who indicated that Hamlin had been suffering from a sinus infection since Friday but that the condition had got much worse on race day.

"It's not just a headache. It's a lot more serious than that. He was actually losing vision [in] his eye," Hamlin's crew chief Darian Grubb explained to MRN.com and NASCAR.com after the race. "He held his head and said his head was hurting so bad. He was having trouble seeing.

"You could tell the worry in his face, he was really upset," he continued. "His vision was getting worse and the pain was getting worse. It got to where he couldn't see and was having trouble with the vision in his left eye because of the pressure and everything that was going on."

Hamlin told the NASCAR medical team about his condition, and they took the decision to pull him from competition: "NASCAR did some testing and he could not follow the finger going by his eyes as he should have been," Grubb confirmed. "They weren't going to let him go [racing.]"

"I think he could still drive, but the problem was he was concerned about it," suggested Gibbs. "He just wanted to make sure it was taken care of. When he brought it up, the doctors said, 'Hey, you have to do this right away. Hopefully it's nothing, but you have to get it checked out.'

Instead, Hamlin was sent to a local California hospital for further evaluation and treatment. He was released later on Sunday evening after undergoing tests. Joe Gibbs Racing said in a subsequent team statement that Hamlin would be further evaluated this week back at a facility in Charlotte, North Carolina.

"So disappointed that I can't compete today," Hamlin tweeted later. "Sorry to all my fans. Thought we had a car that could win today."

Hamlin also ended up in hospital in last year's visit to Fontana, after a last-lap clash with Joey Logano sent Hamlin into a nasty impact with the inside wall and injured his lower back, which saw him sit out the following four races and effectively put an end to his 2013 Chase hopes.

Hamlin's place in the #11 car was taken by Sam Hornish Jr., who is driving a limited schedule for JGR in the NASCAR Nationwide Series and who had been at Fontana as a stand-by driver in case pole sitter Matt Kenseth - Hamlin's JGR team mate - had been called away to attend the birth of his third child with wife Katie which is due this weekend.

Hornish has experience of being called up as a last-second substitute, having replaced AJ Allmendinger at the 2012 Coke Zero 400 after the then-Penske driver was suspended form competition over a failed drugs test. Allmendinger has since been full reinstated after undergoing NASCAR's 'road to recovery' program.

Even so, the sudden call-up caught Hornish off-guard: "I figured there was no way I was getting in a car today," he said. "I was probably not as well-hydrated and well-fed as I would have been if I'd known I was getting in the car."

Hornish said the first thing he knew about it was when he got an urgent text message from Grubb asking him to come to the JGR trailer while he had been chatting with Roger Penske. Hornish went on to finish the race in 17th place, very respectable in the circumstances in what was his first Sprint Cup start since last April's race at Kansas Speedway.

Although Hamlin will not benefit from the championship points the #11 won in Hornish's hands as only the driver who starts the race gets credited with the points, NASCAR confirmed that Sunday's absence will not affect Hamlin's eligibility for the Chase under the new format and will be counted as a medical exemption under the rules.