CHARLOTTE, N.C. — Suspended NASCAR driver AJ Allmendinger said Wednesday that he tested positive for a stimulant and was collecting his medicines and supplements in an attempt to figure out what got him in trouble.

A statement issued by Allmendinger’s business manager did not identify the stimulant and said the driver does not know what caused him to fail the random test conducted June 29. He was suspended Saturday and NASCAR has not revealed the substance, either.

“AJ tested positive for a stimulant. He has no idea why the first test was positive, and he has never knowingly taken any prohibited substance,” said Tara Ragan, vice president of Allmendinger’s Walldinger Racing Inc.  “AJ is collecting his medicines and supplements for testing to determine whether an over-the-counter product caused his positive test.”

Allmendinger is the second Sprint Cup Series driver to be suspended under the NASCAR drug policy implemented in 2009. The 30-year-old Allmendinger has requested his “B” urine sample be tested, and it’s not clear when that will occur.

Allmendinger said Tuesday that he would never knowingly take a prohibited substance.

“Obviously I would never do anything to jeopardize my opportunity here at Penske Racing or to my fellow drivers. I am very conscious about my training and health and would never knowingly take a prohibited drug,” he said.

According to NASCAR’s drug policy, a stimulant is defined as “amphetamine, methamphetamine, Ecstasy (MDMA), Eve (MDEA), MDA, PMA, Phentermine, and other amphetamine derivatives and related compounds.”

In March, Allmendinger signed on as a brand ambassador for “Fuel in a Bottle,” energy and protein power shots owned by Charlotte-based BYB Brands, a wholly-owned subsidiary of Coca-Cola Bottling Co.

There’s been no official link to his positive test and the power shots. The March press release announcing the partnership with Allmendinger described “Fuel in a Bottle” as a booster that “provides a quick energy boost in convenient 2-ounce liquid form. It is packed with B vitamins, is sugar free and has zero calories.”

The power boost includes “essential amino acids that your body needs,” the release said. “Both varieties of Fuel in a Bottle allow consumers to recharge in minutes. Run stronger for hours.”

Among the ingredients listed on the label are L-Phenylalanine and caffeine, which are both mild stimulants.

Jeremy Mayfield, the first driver to be suspended under the policy, tested positive for methamphetamine. He has denied for more than three years that he ever took meth, and blamed the positive test on a mix of an over-the-counter allergy remedy and a prescription for attention deficit disorder.

Rather than go through NASCAR’s recovery program, Mayfield fought in court to have his suspension overturned. He abandoned his bid earlier this year.

Ragan said Allmendinger is working through NASCAR’s process to resolve the issue.

“AJ and all of us at Walldinger Racing respect NASCAR’s testing program, and he has requested that his “B” sample be tested as part of the process of getting to the bottom of this,” she said. “We will have the opportunity to review all of the scientific data surrounding the test following the “B” sample test, but our understanding is that AJ’s test was slightly above the threshold.”

The suspension was announced hours before Saturday night’s race at Daytona International Speedway and Sam Hornish Jr. was hustled in to race in Allmendinger’s place. Penske Racing has already said that Hornish will drive the No. 22 Dodge this weekend at New Hampshire.

The team has not discussed its plans for its first-year driver. Allmendinger was hired in late December after Penske’s sudden split with Kurt Busch opened the highly-coveted seat.

Meanwhile, sports car team owner Michael Shank issued a statement of support for Allmendinger, whom he referred to as “a friend of mine, actually more like a brother.”

Shank and Allmendinger last October partnered to form an IndyCar Series team, but a lack of sponsorship prevented them from fielding a car this season. But Allmendinger has competed for Michael Shank Racing for years in the prestigious Rolex 24 Hours of Daytona sports car race, and in January he anchored the race-winning entry for one of the biggest career victories for both driver and owner.

“I stand 100 percent behind him in this challenging time,” Shank said. “He has stood behind me and been loyal to my team for seven years, even when we let him down he never considered bailing on me and my team. I will certainly never leave him behind when tough times come for him. No matter what happens he will stay my friend and continue to drive for me whenever possible.”