Per Chris B. Haynes of Yahoo Sports, Leonard didn't travel with the team to Phoenix in order to continue rehabbing his injured knee.
Leonard played the first four games of his team's Western Conference second-round playoff series against the Utah Jazz. He averaged 32.5 points and 10.5 rebounds in Games 3 and 4, which ended with Clipper wins to tie the series at two games apiece.
However, the 29-year-old suffered a right knee sprain and was ruled out indefinitely on June 16, per Shams Charania of The Athletic and Stadium.
Charania later updated that report to clarify Leonard suffered an unspecified ACL injury. ESPN's Ramona Shelburne also provided updates on the same day, both on Twitter and during The Jump:
NBA on ESPN @ESPNNBA
.@ramonashelburne on Kawhi: "The fear is that this involves the ACL ... they're calling it a sprain for right now, but they need to do some more imaging to determine [severity] ... The Clippers are prepared to be without him for tonight, and most likely the rest of the series." https://t.co/ZtkI3B4sHs
Later that day, the Clippers upset the Utah Jazz 119-111 in Game 5 of their Western Conference second-round playoff series to take a 3-2 lead in the best-of-seven matchup.
After the game, L.A. head coach Ty Lue provided an update on Leonard:
The Clippers managed to win their last two games against the Utah Jazz without Leonard. They erased a 25-point deficit in Game 6 to earn a 131-119 win, earning the franchise's first appearance in the Western Conference Finals.
Leonard averaged 24.8 points on 51.2 percent shooting, 6.5 rebounds and 5.2 assists per game for the Clippers this season.
The five-time All-Star, two-time NBA champion and five-time All-NBA player is in his 10th NBA campaign.
Terance Mann, who scored 39 points in Game 6 against the Jazz, will likely start in Leonard's spot against the Suns.
Los Angeles and Phoenix will play Game 1 at Talking Stick Resort Arena on Sunday at 3:30 p.m. ET.