Nobody is beyond reproach when it comes to the Dallas Mavericks, not even Dirk Nowitzki.

Owner Mark Cuban said Monday that he’s hoping to see an upgraded effort defensively out of the face of the franchise heading into the stretch drive of the season.

“We’re gaining more confidence in our defense and that’s got to get better,” Cuban said. “We got to get a little more out of Dirk defensively and a little more energy out of Dirk. I think overall, our bench has been great and we’re starting to realize that when we’re hitting shots, we can be unbeatable. And when we’re not, we’re starting to find ways to win. We just got to be better at it.”

Asked specifically what Nowitzki – averaging 21.4 points and shooting .495 from the field – needs to do better, Cuban said: “Sometimes he loses concentration. We got to get past that. I mentioned it to him today. I asked him how his nap was during the game yesterday (at Oklahoma City). He laughed. At least while I was facing him. When I turned and walked away, I don’t know what he did.”

It’s rare for Cuban to call out anybody on the team, much less Nowitzki. He questioned the effort of the entire team during the 2008-09 season when the Mavericks laid a huge egg in a game at Oklahoma City. He also thought they eased off the gas pedal in their championship season when Caron Butler was injured.