Recurrence of blood clots knocks NASCAR driver Brian Vickers out of race car again

Brian Vickers has had a recurrence of blood clots and will step out of his Michael Waltrip Racing ride this weekend at Auto Club Speedway.

Brett Moffitt will return to the No. 55 Toyota as Vickers' replacement.

Vickers missed the first two races of this year following offseason heart surgery.

The blood clots have been a persistent problem: Vickers missed 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.

This latest recurrence has again required Vickers to be placed on blood thinners.