NASCAR driver Brian Vickers will miss this weekend’s NASCAR Sprint Cup Series race at Auto Club Speedway in Fontana, California due to blood clots. Michael Waltrip Racing, the team Vickers drives for, announced the news on Friday.

This is the third time that Vickers has had to deal with blood clots, and the fourth time that he has missed races due to medical issues. Vickers missed the final 24 races of the 2010 season after he was initially diagnosed with blood clots in his legs and lung, and he missed the final five races of 2013 due to blood clots in his leg, ESPN notes. He missed the first two races of this year because of having heart surgery in December. Vickers has been placed on blood thinners and can’t race while on them because it would be too dangerous, according to the Associated Press.

''Thankfully, because I recognized the signs and symptoms, the doctors caught this early and I'm going to be ok,'' Vickers said in a 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.''

Michael Waltrip Racing owner Michael Waltrip said that their thoughts are with Vickers and that Vickers isn’t only their driver but their friend. He also said that Vickers started experiencing the blood clots Thursday night and they don’t know how long he will be out.

Vickers is in his second and final year of his contract with Michael Waltrip Racing. He returned to the Sprint Cup series in the third race of the year at Las Vegas, where he finished 15th. Last week at Phoenix he finished 41st. Vickers has three wins and 12 poles in his Sprint Cup series career, according to Fox Sports.

Brett Moffitt, who filled in for Vickers at Atlanta and finished eighth, will fill in for Vickers at Fontana this weekend. Moffit had been filling in for David Regan at Front Row Motorsports while Regan fills in for the injured Kyle Busch at Joe Gibbs Racing. NASCAR XFINITY Series driver Chris Buescher will drive for Front Row Motorsports in place of Moffitt.