NASCAR Sprint Cup driver AJ Allmendinger has been temporarily suspended by the sanctioning body after failing a random drug test.

NASCAR senior vice president Steve O’Donnell made the announcement Saturday evening at Daytona International Speedway prior to the Coke Zero 400 race.

Allmendinger was scheduled to start ninth in the race. Penske Racing teammate Sam Hornish Jr. was on his way back to Daytona Beach from North Carolina Saturday and is expected to replace Allmendinger in the Penske Racing No. 22 in the 400. He will start from the rear of the field because of the driver change.

According to NASCAR procedures, Allmendinger can request within 72 hours that another sample – the so-called “B” sample – be tested.

O’Donnell did not take any questions after making the announcement in the DIS media center.

NASCAR has a long list of prohibited substances. There was no indication Saturday what triggered Allmendinger’s test failure.

"NASCAR notified Penske Racing this (Saturday) afternoon that AJ Allmendinger was administered a drug test earlier this week, and those results tested positive,” said Penske Racing 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 has been in Sprint Cup racing since 2007 and is winless. This is his first season driving for team owner Roger Penske, and it has been a tough one. Through 17 races, he has only one top-five finish and is 23rd in Sprint Cup points.

Mike Hembree is NASCAR Editor for SPEED.com and has been covering motorsports for 30 years. He is a six-time winner of the National Motorsports Press Association Writer of the Year Award.