Boston Celtics center Kristaps Porzingis is expected to remain sidelined for Games 1 and 2 of the Eastern Conference finals next week, but there's optimism he'll 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 are awaiting the winner of the New York Knicks-Indiana Pacers semifinal series. The Knicks lead 3-2 entering Game 6 Friday (8:30 p.m. ET, ESPN).

Porzingis -- out since suffering 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 Cleveland.

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 points and 7.2 rebounds 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.