By Matt Citak

The Celtics’ season could not have gotten off on a worse note. Before the first quarter of the first game was complete, Boston had lost their big free-agent acquisition, Gordon Hayward, to a gruesome ankle injury. All seemed lost in Bean Town, as Hayward was supposed to help the Celtics finally take down LeBron James and the Cleveland Cavaliers.

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Boston would go on to lose the season opener to the Cavs, along with their second game of the season. But then, led by Kyrie Irving, the Celtics showed the rest of the league their resilience, ripping off 16 consecutive victories and catapulting themselves to the top of the Eastern Conference. They stayed there for a large portion of the season.

Now, with a month until the playoffs, the injury bug has returned to Boston.

Irving, Boston’s top scorer and passer, is currently out with soreness in his left knee due to lingering tendinitis. The injury is not thought to be serious, though the Celtics can’t be thrilled with their best player’s extended absence this late in the season.

Irving is far from the only Celtic relegated to the bench because of injury. Joining the star point guard on the sidelines right now are Marcus Smart, Jaylen Brown, and Daniel Theis, with Al Horford also missing a few games due to illness.

Horford should be back any day, and Irving should also be ready to go far before the playoffs start. Brown is expected to miss some time after suffering a concussion from a nasty fall on his head and upper back against the Timberwolves last week. However the young forward should return to the lineup within the next few weeks. Theis is reportedly done for the season with a torn meniscus, but Greg Monroe should be able to adequately replace the backup big man.

Marcus Smart #36 of the Boston Celtics calls for the ball during the first half against the Los Angeles Lakers at Staples Center on January 23, 2018 in Los Angeles, California.

Marcus Smart (Photo Credit: Harry How/Getty Images)

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That leaves Marcus Smart, and, unfortunately for the Celtics, his absence may be too difficult to overcome.

Smart tore a tendon in his right thumb, and the most recent reports make it seem unlikely that the guard can return this season. If that’s the case, it would be a significant blow to Boston’s chances at making a championship run.

The 6-foot-4 point guard is far from an amazing shooter. Smart is shooting just 36.7 percent from the field this season, and 30.1 percent from the three-point line. But on a team filled with talented scorers, the 24-year-old point guard wasn’t relied upon for his offense.

The value Smart brings to the Celtics is immeasurable. He provides the grit and determination that could end up being the difference between a win and a loss. Smart is the type of player who gives 100 percent effort from tip-off until the final buzzer, no matter the score. He’s fights for every loose ball, and usually wins those fights.

And while he isn’t known for his offensive abilities, Smart has a knack of keeping defensives honest with the occasional strong shooting performance. The perfect example of this occurred during Boston’s loss to the Pacers on Sunday. Smart scored 20 points, shooting 6-for-12 from long range, while racking up eight assists, seven rebounds, and four steals.

There’s no denying the talent Boston has on its roster. Even without Smart, the Celtics still have a solid chance of making the Eastern Conference Finals. But what seemed like a realistic feat just a week ago became a whole lot harder with the loss of the third-year point guard. The team will really have to battle to make a deep playoff run now, and will need some of their other young players to step up.

Boston’s road to the NBA Finals certainly got a lot tougher with the injury to Smart. But as we’ve witnessed this season, no matter who’s out there on the court, the Celtics will not go down without a fight. You can count on that.

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Matt Citak is a contributor for CBS Local Sports and a proud Vanderbilt alum. Follow him on Twitter.