The Boston Celtics begin their quest for Banner 18 on Sunday, but they still don't know who their first-round opponent will be.

The Philadelphia 76ers defeated the Miami Heat 105-104 in their Play-In Tournament matchup on Wednesday night, making them the only team the Celtics won't face to begin the postseason.

The Heat will face the loser of the Chicago Bulls and Atlanta Hawks contest on Thursday, with the winner clinching the eighth and final seed in the Eastern Conference.

With its season on the line, Miami could be without star forward Jimmy Butler for the foreseeable future due to a potential MCL injury in his knee, according to The Athletic's Shams Charania. Butler could be sidelined for an indefinite period of time and an MRI is reportedly scheduled for Thursday.

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Butler was injured late in the first quarter of the Heat-Sixers matchup when he tried to fake out Kelly Oubre Jr. on a shot. His right knee buckled and he fell to the court.

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"I fell, he landed and my knee just didn't do well, I guess," Butler said, per ESPN News. "I don't know. It's not a good feeling, I can tell you that."

In Miami's loss to Philadelphia, Butler scored 19 points and collected four rebounds in 40 minutes of play. This season, he has averaged 20.8 points, 5.3 rebounds, and 5.0 assists for the Heat.

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Butler was instrumental in the Heat defeating the Celtics in the Eastern Conference Finals last season and even went as far as guaranteeing a Game 7 victory after losing Game 6 in Miami.

Featured image via Bill Streicher/USA TODAY Sports Images