The NBA has suspended Phoenix Suns star Deandre Ayton for 25 games after violating the terms of the league's anti-drug program.

It was announced on Thursday that 2018 number one draft pick Ayton had tested positive for a diuretic, with the 21-year-old to serve a ban without pay.

Ayton's suspension will start with Friday's game between the Suns and the Denver Nuggets.

The National Basketball Players Association (NBPA) is already planning arbitration to reduce or rescind the penalty entirely due to Ayton allegedly unintentionally taking the drug, according to reports.

Ayton scored 18 points and added 11 rebounds in Phoenix's season-opening 124-95 win over the Sacramento Kings on Wednesday.

He was named to the NBA's All-Rookie team last season after averaging 16.3 points and 10.3 rebounds.