Michael Waltrip Racing's Brian Vickers has been ruled out of racing in this weekend's Auto Club 400 in Fontana, California after reporting a recurrence of problems with blood clotting.

Vickers had been scheduled to drive the #55 MWR entry in this weekend's NASCAR Sprint Cup Series race, but his place will now be taken up by Brett Moffitt who previously deputised for Vickers in the second round of the season at Atlanta Motor Speedway.

"First and foremost our thoughts are with Brian and his family," said team founder and co-owner Michael Waltrip. "He isn't just our race car driver, he is our friend and we know the NASCAR community will continue to rally around Brian.

"He is more susceptible to clots than you and I are," Waltrip explained. "We knew that could be an issue. Are we surprised? Yes. Did we think it would happen? No.

"We are fortunate to have Brett Moffitt in our system and marvelled at his great drive in Atlanta three weeks ago, so we know he can get the job done in the #55 this weekend," he added. "As this news is very fresh and the situation is very fluid, we can only plan for this weekend at this point."

Vickers has had a series of health problems over the years, dating back to the 2010 season when an initial problem with blood clots ended up in surgery for a hole in the heart that resulted in him having to sit out almost the entire season. He also missed the final races in 2013 with further blood clotting issues.

The 31-year-old driver had to undergo further heart surgery over the winter after it was found that the original patch used in the first cardiac procedure had started to be rejected by his body. Vickers missed the first two rounds of the 2015 season at Daytona and Atlanta while he completed his recovery before returning to action at Las Vegas and Phoenix, where he finished in 15th and 41st positions respectively.

The latest recurrence of blood clotting issues means that Vickers now needs to resume taking blood-thinning medication. Because of the resulting risk of uncontrolled bleeding in the event of an on-track accident, this means he is not able to race while on the medicine.

"Thankfully, because I recognized the signs and symptoms, the doctors caught this early and I'm going to be okay," Vickers said in a statement released by the team just hours before practice gets underway at Auto Club Speedway in Fontana, California for this weekend's race.

"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," Vickers continued. "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.

"I'm disappointed I can't be there but if there is a silver lining in all of this, hopefully what's happened to me will help to raise awareness on this important health issue," he added. "Believe it or not, it's Blood Clot Awareness Month and I was supposed to be at the track this weekend doing some work with my partners at Janssen focused on getting the word out."

In 60 races driving the #55 for MWR, Vickers has notched up eight top-five and 19 top ten finishes. He won the July race at New Hampshire in 2013 and captured the pole at Talladega in October 2014. In total, the 2003 Nationwide champion has three victories and 12 poles in 318 Cup starts.

His replacement for this weekend, Brett Moffitt, had impressed the team by recording a top ten finish in his previous one-off stand-in role in the #55 last month at Atlanta. The eye-catching performance by the 22-year-old saw Moffitt subsequently hired by Front Row Racing to take over the #34 entry from David Ragan, who is currently on loan to Joe Gibbs Racing as a stand-in for Kyle Busch who has himself been sidelined after suffered leg and foot fractures in a NASCAR Xfinity Series support race at Daytona on February 21.

Roush Fenway Racing's Xfinity Series regular Chris Buescher will now take over the #34 Front Row entry this weekend for what will be his Sprint Cup d?but at somewhat short notice. The team had planned to retain Moffitt for further races, but the news about Vickers means that plans for upcoming races for both MWR and Front Row are very much to be determined.

"It's been very hectic, I was actually getting breakfast over by the hotel and [RFR general manager] Robbie Reiser called me," said Buescher. "I was getting ready for an ARCA race and got the call and was rushed to Richmond, so it's been wild. I'm happy to help out Front Row and help out another Ford team.

"We're trying to all work the best we can to make this happen as smoothly as possible," he added."It's gonna be a wild weekend between the two schedules. I'm excited to get the opportunity, so I appreciate that very much, but we're gonna have to be on our toes this weekend.

"I've run a lot of Cup test sessions and throughout the years I've done a lot at Roush Fenway on the Cup side, but this will be the first race. The circumstances that bring it about are not ideal. We wish Brian Vickers the best and want to try to do the best we can for Front Row Motorsports now at this point."

Jamie Dick diagnosed with new onset diabetes

NASCAR Xfinity Series driver/owner Jamie Dick has also been forced out of this weekend's racing action in Fontana with health issues.

The 26-year-old reported to the infield care centre at Phoenix International Raceway last weekend complaining of fatigue and dizziness after finishing 28th in the fourth round of the 2015 season. He was later referred to the nearby West Valley Hospital in Goodyear, Arizona, for further evaluation.

According to the team, Dick was released from the hospital Sunday afternoon and then returned home to Charlotte, North Carolina for further treatment after being diagnosed with new onset diabetes.

"I would like to thank everyone for their support during this difficult time," Dick said in a statement released by the team. "It was quite a surprise to hear the diagnosis from the doctors, but the response from the NASCAR and PIR medical staffs was outstanding.

"The support from the racing community, my Viva Motorsports team, and the fans has been overwhelming," he added. "Now I need to learn about this disease and do whatever it takes to get back behind the wheel as soon as possible."

Jeffrey Earnhardt will take over from Dick in the Viva Motorsports car, which coincidentally is also the #55 entry - the same as Brian Vickers' in the Cup series.