PITTSBURGH -- Defenseman John Ludvig, making his NHL debut, left with an injury at 10:41 of the second period Tuesday in the Pittsburgh Penguins 4-1 loss to the Dallas Stars.

Ludvig, 23, was briefly knocked unconscious following a collision at center ice with Stars forward Radek Faksa.

Claimed off waivers from Florida before the season started, Ludvig lay face down, motionless on the ice for several minutes while trainers and medical staff from both teams attended to him. He was eventually helped to his feet and skated from the ice with assistance from teammates Marcus Pettersson and Noel Acciari.

Penguins coach Mike Sullivan said, after the loss, that Ludvig was being evaluated, and added that "it appeared that he almost got knocked out on the hit."

"It's a scary moment when you see a player like that," Sullivan said. "Those are scary to watch. We're hopeful he's going to be OK."

Later in the third period, Jason Robertson set up Thomas Harley's goal and Wyatt Johnston scored later in the period to help Dallas cruise to the win.

"He was excellent tonight," Stars coach Peter DeBoer said of Robertson. "He's a game-breaking guy. When he's feeling it like he was, you can tell that he was in one of those zones where he was going to be a difference-maker."

Bryan Rust scored the first goal for Pittsburgh, but Dallas had the next four. The Stars haven't lost in regulation yet this season.

The Associated Press contributed to this report.