By Brian Robb, CBS Boston

BOSTON (CBS) – The Celtics have one of the deepest backcourts in the Eastern Conference, and that unit will be put to the test over the next few weeks as second-year guard Marcus Smart remains on the sidelines.

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The 21-year-old suffered a lower left leg injury in Friday’s win over the Brooklyn Nets, and head coach Brad Stevens confirmed on Sunday that the ailment will keep him out of action for at least a couple weeks.

“(It’s a) subluxation of the proximal tib-fib (tibiofibular) joint that from now on will be referred to as a lower leg injury on the left leg,” Stevens told reporters in Brooklyn, according to The Boston Globe. “They say it’s a couple weeks-plus, and there’s no real end beyond a couple weeks. It could be a couple weeks, it could be longer than that, so hopefully it gets a lot better sooner because obviously he’s a big loss for us.”

Smart suffered the injury after colliding with Thomas Robinson in the fourth quarter of Boston’s 120-95 win over the Nets on Friday.

The extended absence comes as the latest blow to Boston’s starting backcourt, which has been riddled with the injury bug throughout the first month of the NBA calendar. Smart already missed three games with a toe injury in the first week of November, while Avery Bradley was sidelined for a pair of contests last weekend with a sprained calf.

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Since returning to full health, Bradley had been able to provide the Celtics with a scoring spark off the bench, but those plans change now with Smart out of the fold. Isaiah Thomas and Bradley will remain the starters for the foreseeable future and Brad Stevens will have to look to Evan Turner and younger guards such as Terry Rozier and R.J. Hunter for support off the bench.

“I think one of our young guys will play some of those minutes,” Stevens said of Smart’s playing time to MassLive. “And we’ll go from there. And hey, that’s why we have a team. That’s why we have guys that are capable of stepping in and helping.”

While the Celtics may benefit from Smart’s absence on the offensive end (due to his 33 percent shooting from the field), there’s no question his defensive presence will be missed. That fact was already evident as Boston allowed the Nets to post 111 points in an ugly Celtics loss on Sunday night.

Boston still remains as a top-five ranked NBA defense, but the ability to sustain that position becomes tougher without Smart harassing opposing guards on the perimeter.

With the Celtics scheduled to face an imposing list of point guards over the next two weeks (John Wall, Derrick Rose, Rajon Rondo, Stephen Curry), Thomas, Bradley and Co. have their work cut out for them to make up for Smart’s presence.

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Brian Robb covers the Celtics for CBS Boston and contributes to NBA.com, among other media outlets. You can follow him on Twitter @CelticsHub.