In a significant blow to the Boston Celtics' hopes of a long postseason run, guard Marcus Smart has suffered a torn left oblique and could miss the opening two rounds of the Eastern Conference playoffs.

Boston issued a statement Wednesday night saying Smart would resume basketball activities in four to six weeks, a timeline that could sideline him through the team's first-round matchup against the Indiana Pacers and, if they advance, a likely second-round matchup against the top-seeded Milwaukee Bucks.

Smart was injured in a home loss to the Orlando Magic on Sunday.

He has played a significant role for the Celtics this season, and a difficult pathway to emerge out of the East only becomes more difficult with the guard's loss.

Smart, 25, has averaged 8.9 points, 2.9 rebounds and 4 assists, but his defense and grittiness separates him, especially in the playoffs.

In Smart's absence, the Celtics will almost certainly revert back to Jaylen Brown as the team's starting shooting guard -- as he was for the opening few weeks of Boston's season. But after the Celtics struggled through the first 20 games of the season, Smart was inserted into the starting lineup, and Boston quickly rattled off an eight-game winning streak. Smart and the Celtics never looked back, and Smart was expected to be an integral part of the team's hopes for a deep playoff run over the next two months.

Brown looked out of sorts early in the season as he tried to adjust to the reintroduction of both Kyrie Irving and Gordon Hayward to the mix in Boston, but Brown has thrived over the past few months coming off the bench. Presuming Brown does, in fact, return to the starting lineup now, Boston will be hoping he can carry that momentum over into the postseason -- though Brown has been dealing with back issues of his own over the past week or so.

Smart, 25, has had a career season for the Celtics, after signing a four-year, $52 million contract as a restricted free agent last summer. He is shooting a career-best 42.2 percent from the field, including another career-best 36.4 percent from 3-point range, and Smart is expected to be named to one of the league's All-Defensive teams for his work alongside Irving in Boston's backcourt.

Smart suffered his injury during the third quarter of Sunday's loss to the Orlando Magic in Boston, a meaningless game for the Celtics, who already were locked into the fourth seed and a first-round matchup against the Pacers, beginning this weekend. And it happened on a strange play, as Smart collided with Magic center Nikola Vucevic while chasing Evan Fournier down the lane, then crashed to the ground, holding his side.

Boston eventually called a timeout, and Smart limped to the bench -- only to convince the training staff that he was all right and could stay in the game. But after the Celtics had the ball for one offensive possession -- on which Smart was clearly moving gingerly -- Smart called for the bench to replace him as he limped back on defense before falling to the floor, writhing in pain and holding his side. Eventually, he got to his feet and, with the help of trainers, hobbled to the locker room.

ESPN's Tim Bontemps contributed to this report.