Sources: Celtics' Kristaps Porzingis expected out for start of ECF

Boston Celtics center Kristaps Porzingis is expected to remain sidelined for Games 1 and 2 of the Eastern Conference finals, but there is optimism he will be able to return sometime in the series barring any setbacks, sources told ESPN on Friday.

Porzingis has been making progress in his recovery from a soleus strain of his right calf, ramping up his on-court activity for an anticipated return in the conference finals, but still needs more time for a return to play, sources said.

The Celtics will face the Indiana Pacers in the finals.

Porzingis -- out since sustaining the injury in Game 5 of the Celtics' first-round series against the Miami Heat on April 30 -- missed the entirety of Boston's five-game conference semifinal series victory over the Cleveland Cavaliers.

He is likely to miss the opening two games of the East finals, scheduled for Tuesday and Thursday in Boston.

At 7-foot-3, the return of Porzingis -- who averaged 20.1 points and 7.2 rebounds per game in the regular season -- is considered paramount for the Celtics' ultimate chances of winning a championship.

Al Horford, 37, has been starting in Porzingis' place. Horford had a remarkable 22 points, 15 rebounds, 5 assists and 3 blocks in the series-clinching win over Cleveland on Wednesday.

Porzingis arrived in Boston via an offseason three-team trade with Washington and Memphis.