Are the Mavericks in trouble?

The Mavericks have been struggling lately, and they're going to have to clean things up if they're going to remain in the West's top eight.

The Dallas Mavericks are in a tough spot. They added Jose Calderon and Monta Ellis in the offseason to improve their offense, but the new backcourt also ensured their defense would remain shoddy. Even with a terrific season from the 35-year-old Dirk Nowtizki, the 20-16 Mavericks have a tenuous grip on the eighth seed in the West, with the Denver Nuggets and Minnesota Timberwolves on their heels. While Mark Cuban and co. have their sights set on the playoffs, Dallas' last couple of weeks have not been encouraging.

After winning five of seven games to start December, the Mavericks have lost six of their last 11. In those games, they have given up 106.7 points per 100 possessions, per NBA.com. That number jumped to 112.3 per 100 when forward Shawn Marion -- the only Dallas starter you can credibly call a good defender -- went to the bench.

It's awful news, then, that Marion is banged up. Entering their game against the Los Angeles Lakers on Tuesday, he was questionable with ankle and achilles issues. He ended up playing, but before halftime he took a hard fall and bruised his right shoulder and upper ribs. Dallas went on to beat a decimated Lakers squad without Marion, but he had to stay home when the team set off on its two-game trip to San Antonio and New Orleans.

The Spurs game on Wednesday went about as poorly as you can imagine, with the Mavericks surrendering 37 points in the third quarter and suffering a 112-90 blowout loss.

"The third quarter was a demolition," head coach Rick Carlisle told reporters, adding that his team was outcompeted by San Antonio.

Mavs Moneyball: Spurs crush Mavs

Seeing as the Spurs have now beaten Dallas seven times in a row by an average of 16.7 points, via ESPN Dallas, it's disheartening that San Antonio looks like the Mavericks' likely first-round opponent if they can even hold on to a playoff spot.

The loss to the Spurs wasn't Dallas' worst, though. The worst was last Sunday against New York. The Knicks, who were without defensive anchor Tyson Chandler for all but the first four minutes, held the Mavericks to 35 points in the first half. That was the game in which Marion sprained his ankle and hurt his achilles, and New York ended up winning by a score of 92-80.

"You can never relax in this league," Nowitzki said following the loss to the Knicks, via ESPN Dallas. "First of all, we're not even good enough to relax. We've got to bring it every night. We've got to compete every night, both ends of the floor, for us to have a chance. We're not talented enough to coast on either end of the floor."

Therein lies the challenge for the Mavs, who were winning earlier in the season because of their effectiveness in their halfcourt offense and in transition. Without a solid defensive foundation to rely on, they do not have much room for error. They can't often afford for Calderon to shoot 2-for-11, like he did in San Antonio, or to shoot 6-for-26 from the three-point line collectively, as they did against the Knicks.

Between now and next Saturday, Dallas will play the Pelicans twice, then the Magic, Clippers, Suns and Trail Blazers. That's a tough stretch, especially if Marion has to miss extended time. If this is indeed a playoff team, the Mavericks are in need of a major turnaround.