The Boston Celtics will begin defence of their NBA championship without the services of standout center Kristaps Porziņģis.

Porzingis underwent surgery for a left ankle injury that sidelined him for much of the Celtics' run through the NBA Finals, the team announced Thursday. The one-time All-Star is expected to need five-to-six months of recovery time, which could delay his season debut into December.

The Celtics said in a statement that Porzingis' procedure was to repair a torn retinaculum and dislocated posterior tibialis tendon in his left ankle, an injury he sustained in Boston's win over the Dallas Mavericks in Game 2 of the Finals on June 9.

Porzingis sat out Games 3 and 4 before returning for a limited role in the Celtics' title-clinching 106-88 victory in Game 5.

The eight-year veteran previously missed 10 play-off games with a strained right calf before returning for Game 1 of the Finals.

Porzingis will also miss next month's qualifying tournament for the Summer Olympics in Paris, where he was to compete for his native Latvia.

Acquired from the Washington Wizards last June as part of a three-team trade that sent former NBA Defensive Player of the Year Marcus Smart from Boston to the Memphis Grizzlies, Porzingis played a major role on a Celtics team that compiled the league's best regular-season record at 64-18 before going on to capture the franchise's first championship since 2008.

The 7-foot-2 Porzingis ranked third among Boston players in scoring at 20.1 points per game, shot 37.5 per cent from 3-point range and also averaged 7.2 rebounds in 57 games.

Porzingis, an All-Star with the New York Knicks in 2017-18, was limited to just seven games this post-season and averaged 12.3 points and 4.4 rebounds.

The 28-year-old is under contract for one more season after signing a two-year, $60 million extension shortly after last summer's trade.

Porzingis' injury will likely push veteran Al Horford into a starting role to begin next season. The 38-year-old Horford averaged 9.5 points, 6.9 rebounds and 2.3 assists while starting Boston's final 15 post-season games and recently said he intends to return for an 18th NBA season.