The junior from Riverside, California, announced his plans on his Instagram account Wednesday.
"Thank you to UCLA and coach (Mick) Cronin for believing in me," Clark's post read. "I'd like to announce that I am declaring for the 2023 draft."
Clark didn't indicate whether he would hire an agent ahead of the June 22 draft or retain his remaining eligibility. He has until May 31 to withdraw and be able to return to Westwood.
He suffered a lower right leg injury in the regular-season finale against Arizona on March 4. Clark averaged 13 points and six rebounds while starting 29 of 30 games. He led the Pac-12 in total steals with 78, tying for third all-time in single-season steals for the Bruins.
He was a second team All-Pac-12 selection, was named the league's defensive player of the year and made its five-man All-Defensive Team.
With Clark out, UCLA lost the Pac-12 conference tournament final to Arizona and were bounced from the NCAA Tournament by Gonzaga in the Sweet 16.