Just hours before the start of Saturday night's Coke Zero 400 at Daytona International Speedway, NASCAR announced that Sprint Cup Series driver A.J. Allmendinger has been "temporarily suspended" from competition for violating the sanctioning body's substance abuse policy.

According to NASCAR, Allmendinger was suspended "based upon notification of a positive 'A' test NASCAR received from the Medical Review Officer as stated in Section 19-11B (6,7) of the NASCAR Substance Abuse Policy."

NASCAR also noted, "Pursuant to the rule book, Allmendinger has the opportunity to request within the next 72 hours that his "B" sample be tested.

Penske Racing immediately called upon Sam Hornish Jr. to replace Allmendinger in the No. 22 Dodge for the 400-mile race at Daytona. Hornish, who drives for Penske full-time in the Nationwide Series, arrived at the racetrack moments before Grand Marshal and former Florida State football coach Bobby Bowden gave the command to start engines.

Hornish had to start from the rear of the field. Allmendinger had qualified eighth on Friday.

"NASCAR notified Penske Racing this afternoon that A.J. Allmendinger was administered a drug test earlier this week, and those results tested positive," Penske Racing said in a statement. "NASCAR has a strict drug testing program that Penske Racing fully supports. Penske Racing will work with NASCAR through this process and its next steps. Sam Hornish Jr., will drive the No. 22 car in tonight's Coke Zero 400."

Allmendinger, 30, is the second Sprint Cup driver to be suspended since NASCAR revised its drug policy prior to the start of the 2009 season. Jeremy Mayfield failed a drug test in May '09 and has not competed in a NASCAR event since then.

Last December, Allmendinger signed with Penske Racing to replace Kurt Busch in the No. 22 car. Allmendinger is currently 23rd in the Sprint Cup point standings, with just three top-10 finishes. He has yet to win a race in NASCAR's premier series.