FONTANA, Calif. — Brian Vickers has been sidelined again by blood clots that prevent him from safely driving a race car.

Vickers’ third bout with blood clots was announced Friday by Michael Waltrip Racing, which replaced him with Brett Moffitt for Sunday’s NASCAR race at Auto Club Speedway.

“We support Brian,” said Michael Waltrip, the team founder and co-owner. “We love his heart. We love who he is.”

The 31-year-old driver must go back on blood-thinning medication, which makes it too dangerous to race. If Vickers got injured in the car, any bleeding would be difficult or impossible to stop.

“He’s in the care of his doctors and expects to be able to operate normally today,” Waltrip said. “That’s really all the information I have on what his current state is, other than he feels really good and he’s really sad.

“If he wasn’t a race car driver, you wouldn’t know there was an issue. He would be on blood thinners, but he has to be off them to drive the car, and that hasn’t worked out.”

Waltrip and Vickers were in New Orleans together on Wednesday for a sponsor event before traveling Thursday to the Los Angeles area. MWR General Manager Ty Norris learned of Vickers’ condition early Friday morning.

“He’s getting the right treatment,” Norris said. “As a human being, he’ll be fine moving forward, and that’s the most important thing.”

Norris declined to say where Vickers’ blood clots were located. Waltrip’s team has only preliminary information about Vickers’ condition, but the driver is in the care of doctors in Los Angeles.

Moffitt will return to the No. 55 Toyota this weekend after driving it to an impressive eighth-place finish at Atlanta.

Waltrip said the team has no idea how long Vickers will be sidelined, but the 22-year-old Moffitt will drive the car “for the foreseeable future.”

Although Vickers has been sidelined by medical issues for the fourth time in his NASCAR tenure, Waltrip wouldn’t speculate on whether Vickers’ racing career is over.

“He would not say that, and therefore I can’t say that,” Waltrip said.

“I guarantee you he would tell you he’ll be back.”

Vickers missed the first two races of this year following offseason heart surgery to repair a patch on a hole in his heart that his body was rejecting. The heart issue was first discovered in 2010 when Vickers was sidelined with his first bout with blood clots.

The blood clots caused Vickers to miss the final five races of the 2013 season because he was placed on blood thinners to treat a clot in his right calf.

He also missed 25 races during the 2010 season when clots were discovered in his legs and lungs.