Marleau said he did not realize Haula was injured until he turned around to look after heading toward the bench. The game was delayed for about 10 minutes while Haula was attended to on the ice.
"Rubbed him out after he dumped the puck in," Marleau said. "I turned to go to the bench when I heard the whistle go. I turned around and he was on the ice. I just hope he's OK. It's a weird thing to see, obviously. Can't help but think about it. You just hope he's OK. You still have to play and try to get the two points."
Haula waved to the crowd when he was removed from the ice with 14:59 remaining and Vegas trailing 2-1. He had one shot in 13:07 of ice time.
The 27-year-old had NHL career highs of 29 goals, 26 assists and 55 points in 76 games for Vegas last season.
"Yeah, that's tough, you don't want to see that," Golden Knights forward Cody Eakin said. "He's a big part of our team."