Josh Norris is out at least two weeks with a shoulder injury.
The Senators are waiting for results on an MRI performed on the forward, who left a 6-2 victory against the Arizona Coyotes on Saturday midway through the third period after he was injured taking a face-off.
"There's just so much torque that goes into these face-offs, and guys are digging in," coach D.J. Smith said. "It's unfortunate. We were lucky that no one had gotten banged up so far, and then this takes a piece from us. But in saying that, it's Derick
(18:32) and Alex DeBrincat (18:29).
Brassard made his season debut and scored for the Senators in a 4-2 win against the Dallas Stars at Canadian Tire Centre on Monday. He played center on a line with forwards Claude Giroux and Alex DeBrincat, and took Norris' place on the power play.
"You never know when you're going to have to jump in," Brassard said. "A situation like that, you see an injury, it's not the perfect scenario, but we're a team here, everyone's important. The extra guys, we've worked hard the past two weeks to try and stay ready.
"When your team is winning, it's pretty easy. It's a great atmosphere in our room. We're having fun every day and everyone wants to play, but at the same time, it's something that I was OK with at the start of the season, accepting my role. That's why I came back, for a situation like this."