From Doc Rivers’s gamesmanship to their own shortcomings, the Celtics have plenty of reasons to not take the 76ers lightly

James Harden (left) will have to take on more of the offensive load if Joel Embiid can't play.Tim Nwachukwu/Getty

The Celtics’ brass is familiar with Doc Rivers’s ability to stretch the truth and conduct gamesmanship. They have no idea about the condition of All-Star center and MVP candidate Joel Embiid entering the latest edition of their epic rivalry, beginning Monday at TD Garden.

Boston and Philadelphia have been targeting each other for an Eastern Conference semifinal matchup for months, knowing they were two of the three best teams in the conference. The other team in that conversation, the Milwaukee Bucks, was eliminated by the Miami Heat, leaving the path to the NBA Finals seemingly more manageable for the winner of this series.

Embiid tweaked his right knee in Game 3 of the first-round series against the Brooklyn Nets and missed Game 4. He was diagnosed with a lateral collateral ligament sprain and is listed as doubtful for Game 1 against the Celtics. Embiid is among the league’s most dominant players and had a 52-point performance against Boston last month. A less than 100 percent Embiid, who has been beset with injuries during the postseason in recent years, could greatly affect the series.

“I’m more certainly preparing for them to have Embiid,” forward Jaylen Brown said. “I definitely think Atlanta made us have to fight. Atlanta brought the fight to us. That’s something you’re going to need going into these playoffs.”

There are three factors that should force the Celtics to remain laser-focused: They have a history of struggling against shorthanded teams this season; a hobbling Embiid is still good for 25 points and 10 rebounds; and Boston’s six-game, first-round series should serve as a warning about how difficult playoff runs truly are.

The 76ers pose different challenges than the Hawks. They are a more veteran team but not as athletic. James Harden, 33, is a top-75 player, former MVP, and one of the more prolific scorers of this generation, but he’s more of a distributor at this point in his career.

Tyrese Maxey is the speedy, high-scoring shooting guard who can get to the rim in a flash and also knock down the 3-pointer. But he shot just 35.4 percent and averaged 10 points in four meetings against the Celtics this season.

Philadelphia is No. 1 in 3-point percentage but 16th in attempts and 12th in makes. It relies so heavily on Embiid’s points in the paint that 3-pointers are not a high priority. That may have to change for the 76ers to have a better chance to win this series.

“Their ability to score in different ways, as much as it’s about Harden and Embiid and how good those guys are, like Maxey and [Tobias] Harris and [P.J.] Tucker are really, really good,” Celtics coach Joe Mazzulla said. “They’re a well-balanced team and we have to make sure we do a great job of the details, keeping them off the free throw line and then managing the game.

“They have a really good team that has an identity even when [Embiid‘s] not in so we have to make sure we understand those tendencies.”

What does Doc Rivers have in store for his old team?Matthew J Lee/Globe staff

The 76ers are a veteran club that relies on the girth of Embiid, playmaking of Harden, speed of Maxey, and shotmaking from their complementary players, such as Harris, Georges Niang, De’Anthony Melton and Tucker. The Celtics won three of the four meetings because they have been better offensively, especially from the 3-point line.

And the 76ers don’t have suitable defenders in the starting lineup for Jayson Tatum or Brown. Harris is bigger than Tatum and will provide resistance. The 37-year-old Tucker is more of a physical defender but would need Embiid as support in case he gets beat off the dribble.

The 76ers are determined to prove they are a different team than in years past. And the pressure may be on Rivers to win this series or risk major changes after the team invested in acquiring Harden and compiling what they believed was a championship-caliber team around Embiid.

There is concern and anxiety in Philadelphia about this matchup, especially with an injured Embiid. Meanwhile, the Celtics are hoping they learned something about themselves after the Atlanta series and use that knowledge — and their desire to return to the NBA Finals — to take control of this series early.

“We got some warriors and some tough guys in this locker room,” Brown said. “Some guys that have handled adversity well and don’t back down from challenges, not afraid of the moment. You get reminded of that during the playoffs when you get into these pressure situations and get to the time where the game is on the line. That’s where you see what someone is made of.”

This will be a familiar challenge for the Celtics because they have faced Philadelphia so many times in the past decade. This is the third time in six years they have met in the playoffs and the Celtics are 8-1 in those previous meetings. The 76ers prepared vigorously for this matchup, disposing of the Nets in the first round, looking impressive in the process until Embiid came up gimpy.

It won’t surprise the Celtics if Embiid is standing midcourt at TD Garden for Game 1. But whether he’s there shouldn’t affect their approach for this series. This will be a considerable challenge, regardless of whether Embiid is 100 percent.