Brian Vickers will miss the remainder of the NASCAR Sprint Cup season after a blood clot was detected in his right calf.
The Michael Waltrip Racing driver will be placed on blood thinners to treat the clot, which was discovered during a medical examination on Monday.
Vickers missed the final 25 races of the 2010 season due to blood clots and heart surgery.
Doctors expect the 29-year-old to be able to race again in 2014.
"If there's anything to be positive about with today's news it's that this is only a temporary setback," Vickers said.
"The timing for this is never good, but I'm glad we'll get it out of the way now."
Vickers extended his part-time MWR programme to a full-time drive in August after Mark Martin decamped to replace the injured Tony Stewart for the remainder of the season.
The team had already planned to run Michael Waltrip in its #55 car at Talladega this weekend, and is yet to decide on a replacement for the remaining four races.
Joe Gibbs Racing is also yet to announce who will drive the car that it runs for Vickers in the Nationwide Series.