Exactly how the prohibited steroid Drostanolone came to be present in Andrea Iannone's urine samples at last year's Malaysian MotoGP still remains unclear.

But the Court of Arbitration for Sport's decision to side with WADA and extend the FIM's initial 18-month ban to four-years effectively ends the 31-year-old's MotoGP career.

Regardless of whether the anti-doping violation was accidental or deliberate, two of those that rode alongside Iannone at Ducati expressed regret that one of the most talented riders of the current generation will not be seen on the grid again.

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Countryman Danilo Petrucci joined Pramac Ducati in 2015, taking over the seat vacated by Iannone when he was promoted to the factory squad.

"I feel very sorry for Iannone," Petrucci said. "First of all, it's not really a good thing to wait one year to have the [final] response of everything.

"But I am just sorry for the man, for Andrea, because he is one of the biggest talents I ever met on track. I'm so sorry not to see him anymore on the track."

Iannone's move to the official Ducati team (where he would claim the factory's first victory since Casey Stoner) came at the expense of Cal Crutchlow.

The Englishman has been one of the most vocal in wanting stricter doping tests in MotoGP. Nonetheless, having seen Iannone's data throughout the 2014 season, Crutchlow has nothing but praise for the Italian in terms of riding talent.

In contrast to his 'Maniac' nickname, it was the #29's smoothness that most impressed Crutchlow, especially the way he cleverly combined use of the throttle and brakes.

"I raced with him at Ducati and Andrea's riding style, the way he rode the bike and the smoothness – honestly there is not really another rider that can do the things he did on a motorcycle," Crutchlow said.

"Yes, Marc [Marquez] is a lot different and very special in another way, but in smoothness of opening the throttle and how he overlapped [the throttle and brakes] was incredible. So, it is a shame to see that he won’t be racing.

"With regards to the penalty or the ban he was given it is not for me to comment… My opinion is that you have to respect the decision that’s been given."

'We all know the rules'

Jack Miller, following the path taken by Iannone and Petrucci in moving from Pramac to the factory Ducati team next season, said he found Iannone's meat-contamination defence hard to believe.

"If you’re asking if it came from meat, I’m going to say no because… We have cows on our farm. Quite clearly we are not injecting them with steroids [but even if we did] and you ate the steak, I don’t think you’d be testing positive for doping," said the Australian.

"To receive that four-year penalty it must’ve been a strong case against him. I wish him all the best. We’ll see what’ll happen, but at this point it doesn’t look great. We all know the rules, what we can and can’t do."

Miller, who said he's been tested "once or twice every year I’ve been in MotoGP" added that he's "100%" aware of what is and isn’t allowed.

"Especially this year," he said. "I had to sit and do a nearly 3-hour course through WADA to apply for my license. I had to read about different ways of avoiding [an anti-doping violation], of the different things you get done for. You know what you can and can’t take.

"I’m paranoid about protein supplements. Some cross contamination can get you. I try to avoid these things. I take things I know are 100% clean and limit them as much as possible. Small mistake can cost a lot. Rules that are in place are for that."

However, Miller also drew a comparison between Iannone's harsh penalty, even though deliberate use was unproven, with the decision not to punish any of the Yamaha riders for the factory's infringement of the engine homologation rules. Instead, Yamaha was docked constructors' and teams' points.

"Iannone got [punished] because he used something that was not allowed. Whether it was intentional is another story. But the ruling given to Yamaha makes it unclear," Miller said.

The CAS decided that Iannone had committed an Anti-doping violation on the grounds that he "failed to establish neither the precise type of meat he had consumed nor the origin of said meat" while his defence experts were also unable "to establish specifically that there was an issue of meat contamination by Drostanolone in Malaysia."

The length of the former Ducati, Suzuki and Aprilia rider's ban could have at least been limited to two years if the anti-doping violation could be shown to be unintentional "on a balance of probability."

However, while "not ruling out the possibility that Andrea Iannone’s [anti-doping violation] may be the result of consumption of meat contaminated by Drostanolone", the CAS Panel concluded that Iannone "has not been able to provide any convincing evidence to establish that the [anti-doping violation] he committed was unintentional."

Iannone's ban expires on 17 December 2023.

His factory Aprilia seat was taken by test riders Bradley Smith and Lorenzo Savadori during 2020, with one of the pair also getting the ride for 2021.