Fontana, CA (SportsNetwork.com) - Michael Waltrip Racing revealed on Friday that Brian Vickers, driver of the No. 55 Toyota, will miss this weekend's race at Auto Club Speedway after he experienced a reoccurrence of blood clots, requiring him to begin taking blood-thinning medication.

Brett Moffitt will drive the No. 55 car in place of Vickers in Sunday's Auto Club 400.

This will be the fourth time that Vickers has been sidelined due to a medical issue.

"He's in the care of his doctors and expects to be able to operate normally today," team co-owner Michael Waltrip said during a press conference on Friday at Auto Club Speedway. "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."

In 2010, Vickers was diagnosed and treated for blood clots in his left leg and both lungs, which had put him out of competition for a majority of that season. Then in 2013, Vickers missed part of the season after he was placed on blood-thinning medication to treat a blood clot in his right calf.

Vickers underwent open heart surgery in December when doctors discovered that his body was rejecting a patch that was surgically placed over a hole in his heart in 2010. The 31-year-old driver was forced to miss the Feb. 22 season- opening Daytona 500 and the March 1 race at Atlanta.

He returned to competition the second weekend in March at Las Vegas, where he finished 15th. He placed 41st in last Sunday's race at Phoenix after being involved in a crash with Jimmie Johnson on the third lap.

Vickers was being treated by doctors in Los Angeles on Friday.

"Thankfully, because I recognized the signs and symptoms, the doctors caught this early and I'm going to be OK," Vickers said in a team statement. "I had finished my treatment for the clot I had in my leg back in 2013, and I haven't needed to be on a blood thinner for a clot in my leg or lung since. Now I won't be able to race because I'll need to be back on a blood thinner. I'm going to follow doctor's orders and do everything I need to do to get well."

Waltrip drove Vickers' car to a 26th-place finish in the Daytona 500, while Moffitt had an impressive eighth-place run at Atlanta.

It is not known at this time how long Vickers will be out of the car.

"We support Brian, we love his heart, we love who he is and we don't know how long he will be sidelined," Waltrip said. "This is all very fluid and new information, and we're learning as we go. But we've elected again, of course, to put Brett Moffitt in the car. Brett was a wonderful replacement driver when he drove for us at Atlanta ... We expect that Brett will race the car competitively."

Waltrip noted that Moffitt will be behind the wheel of the No. 55 for the "foreseeable future." Moffitt was scheduled to drive the No. 34 Ford for Front Row Motorsports at Fontana. Front Row announced that Chris Buescher, a regular in the Xfinity Series, will take over the wheel of the No. 34 in this race.