Arizona guard Allonzo Trier, right, sits courtside as teammates warm up before facing Oregon State last Thursday (AP)

Arizona basketball star Allonzo Trier may have a tough time winning his last-ditch appeal to restore his college eligibility.

Experts on performance-enhancing drugs challenged Trier’s explanation for his second failed drug test, arguing that it’s doubtful the traces of a banned substance found in his system last month are actually remnants left over from when he first tested positive in 2016.

Attorney Steve Thompson told Yahoo Sports last Thursday that both Trier’s positive tests were for Ostarine, a chemical compound that mimics the muscle-building and fat-burning effects of anabolic steroids. Thompson said Trier originally ingested the banned substance inadvertently before the 2016-17 season when his stepfather mixed it into a drink.

Don Catlin, founder and former director of the UCLA Olympic Analytical Laboratory, questioned whether it was plausible for a detectable amount of Ostarine to stay in an athlete’s system for more than 400 days. It added to Catlin’s skepticism that Trier passed multiple random drug screenings in between the NCAA lifting his 19-game suspension 13 months ago and his most recent positive test in late January.

“If the original positive finding was indeed due to inadvertent use of Ostarine in a drink provided by Trier’s father, as opposed to purposeful use of an Ostarine supplement by Trier, then it would be highly unlikely that he would test positive a year later from the original inadvertent use,” Catlin told Yahoo Sports. “Certainly a number of negative results in between support the conclusion that the most recent positive was not connected to the original inadvertent use.

“While hydration, which can affect pH of a urine sample, could be a factor and can influence results, it would not seem a very plausible explanation for a positive drug test occurring a year after inadvertent use of Ostarine. The pH of the negative samples in between could be compared to that of the original and recent positive to evaluate that further.”

Thompson did not return a message from Yahoo Sports sent Monday seeking specific information comparing the amount of Ostarine found in the initial positive test and the most recent one. He said last week that “Allonzo has never been a drug-cheat” and that the minuscule amount of Ostarine found in his system last month “creates absolutely zero competitive advantage.”

Trier has already missed Arizona’s games at Oregon and Oregon State since the NCAA notified the university last Thursday that it had declared the preseason All-American guard ineligible. The only way Trier can win back the right to play for the Wildcats is by persuading an NCAA appeals panel to reduce or eliminate his punishment.

If Trier doesn’t return in time for the postseason, it would be a massive blow to an Arizona program already reeling from allegations that an FBI wiretap intercepted head coach Sean Miller discussing a $100,000 payment to prized freshman Deandre Ayton. Trier, Arizona’s second-leading scorer behind Ayton, averages 19.6 points per game and shoots 43 percent from behind the arc.

David Ferguson, professor of medicinal chemistry at the University of Minnesota, said Trier faces an uphill battle to win his appeal.

Ferguson ruled out a potential procedural error by the drug testing facility since Trier’s attorney likely would have publicized the result of an independent screening exonerating him by now. The dehydration theory Thompson has floated doesn’t hold much merit to Ferguson either because Trier has now had ample time to down as much water as he pleases before retesting himself.

That leaves Ferguson considering two weird possibilities: Trier taking the same drug a second time knowing he’s going to get tested or a trace amount of Ostarine reappearing in Trier’s body out of nowhere despite multiple negative tests since the original ingestion. Ferguson noted that Ostarine typically has a half life of approximately 24 hours, meaning that the amount in the average person’s system should reduce by half each day until it exponentially decays and clears from the body.

“Some people have different levels of enzymes to process drug molecules and things can linger longer, but even if he has deficiencies in his clearance, it wouldn’t go to zero and then come back,” Ferguson said. “That’s highly unlikely unless there was something really odd going on.”

Doctors Duane Miller and James Dalton created Ostarine about 20 years ago in hopes that it would combat muscle atrophy that affects cancer patients and treat the withering of old age. The unsanctioned drug has not been sufficiently tested to be sold legally for human consumption, but dozens of websites peddle Ostarine and other selective androgen receptor modulators (SARMs).

The product has obvious appeal for athletes and body builders because of its muscle-building and fat-burning properties. It accelerates muscle growth without the hair loss, skin problems and excess estrogen associated with testosterone and anabolic steroids.

“You do research to pick that drug,” Ferguson said. “You don’t pick that one by accident. That particular drug is pretty good at targeting muscle and bone and not causing the side effects of anabolic steroids. You don’t get enlargement of your breasts, you don’t get changing of your voice.”

Not long before Trier originally ingested Ostarine, he was reportedly involved in a serious car accident. ESPN.com reported last year that someone close to him gave him the drug without his knowledge to help him recover from injuries suffered in the accident.

Trier walked a well-worn path by insisting that he had unknowingly ingested a banned substance after his original failed drug test. Many college athletes who test positive for PEDs make the same argument because the NCAA all but encourages it.

On a page detailing its drug-testing appeals process, the NCAA lists three paths to a reduced punishment. One is arguing that a procedural error was made during the collection or testing process. Another is demonstrating that the athlete asked “specific and reasonable questions about a particular substance,” but an athletic administrator erroneously responded that the substance did not include a banned ingredient. The third is providing evidence that the athlete was not aware and could not reasonably have suspected that they had been administered the banned substance by another person.

“One of the weaknesses in the NCAA appeals process seems to be that athletes have incentive to invent a reason why they tested positive,” said Oliver Catlin, Don’s son and the president of Banned Substances Control Group. “The structure of the appeals process is outlined in such a way where inventing a reason would be much more likely to lead to a reduction in sanctions than trying to lay the truth out. That bothers me.”

Trier avoided a season-long suspension last year by arguing he had been “given a banned substance by a well-intentioned, but misguided person not associated with the University after an injury.” He returned after 19 games last January because that was when tests showed the Ostarine he ingested had fully cleared his system.

Why it’s back now is a mystery, one that Trier needs to find a credible explanation for as soon as possible. Otherwise when Arizona competes in the NCAA tournament next month, he’ll be on the bench instead of the floor.

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Jeff Eisenberg is a college basketball writer for Yahoo Sports. Have a tip? Email him at daggerblog@yahoo.com or follow him on Twitter!