Phoenix Suns center Deandre Ayton, the No. 1 overall pick in the 2018 NBA draft, has been suspended for 25 games for violating the NBA-NBPA's anti-drug policy with a positive test for a diuretic, the league announced Thursday night.

The National Basketball Players Association plans to file arbitration papers immediately on behalf of Ayton, believing that there will be a case to have the penalty reduced or rescinded based on a collective bargaining agreement provision of "unintentional ingestion," league sources told ESPN.

Diuretics are banned because they can mask performance-enhancing drug use. Sources with knowledge of Ayton's testing told ESPN that follow-up testing on him showed no traces of any other banned substances.

The NBPA has the ability to expedite two cases a year with the league, and sources say it's likely the union will use one of them on Ayton to try to get him back on the court as soon possible.

The timing is terrible for the Suns, who beat Sacramento on opening night Wednesday behind 18 points, 11 rebounds and 4 blocks by Ayton.

Ayton would lose $2.17 million over a 25-game suspension.

"I want to apologize to my family, the entire Suns organization, my teammates, partners, our fans and the Phoenix community," Ayton said in a statement. "This was an unintentional mistake and unfortunately I put something in my body that I was completely unaware of.

"I do understand the unfortunate impact that this has on so many others, and for that I am deeply sorry. I'm extremely disappointed that I've let my team down.

"I will continue to work with the NBPA to go through arbitration and am hopeful of a positive resolution."

The team also issued a statement.

"On behalf of the Phoenix Suns organization, (coach) Monty Williams and I are disappointed in the actions by Deandre Ayton that led to his testing positive for a banned diuretic and subsequent suspension by the NBA. This does not uphold the standards and principles we have set for the team,'' Suns general manager James Jones said.

"Deandre has expressed his deepest remorse. While he is suspended we remain committed to his growth and development on and off the court. His actions are not taken lightly, and we are committed to ensuring that Deandre understands the profound impact it has had on the team, organization, and Suns community.''