Montreal will play the Vegas Golden Knights, with the winner advancing to the Stanley Cup Final. Game 1 of the best-of-7 series is Monday.
Romanov, a 21-year-old rookie defenseman, made his NHL postseason debut in Game 4 of the second-round sweep of the Winnipeg Jets with one shot and one hit in 9:27 of ice time.
"He showed some good composure and made some good decisions with the puck," Canadiens coach Dominique Ducharme said Thursday. "Overall, he was in good position. We like his energy. At the same time, it's important to manage that and [use] it the right way, and I think he did that. So we're happy with the way he's progressing."
Petry missed Game 4 of the second round with an upper-body injury Monday. The defenseman was averaging 23:52 of ice time in 10 Stanley Cup Playoff games, third on the Canadiens behind Shea Weber (25:22) and Ben Chiarot (25:13).
"Now it's more about how Jeff is feeling," Ducharme said. "It's not about when [the semifinals are] going to start. It's really where he's at right now. I don't think one day will be making a difference. If [Petry] is not in the first game, it might be more a question of three or four days after. It's not an overnight thing."
Romanov said he understood why he was a healthy scratch for Montreal's first 10 playoff games after playing 54 regular-season games.
"So difficult," Romanov said. "When guys come to step on our ice and the rink is full of fans (2,500 at Bell Centre), oh my God, tears on the eyes. When I sit in the rink and just look at this, that's hard. It's just the coach deciding, and I trust the coach.
"For me, it doesn't matter where I'll be playing, left (side), right, forward, goalie. I just want to help my team, every single game, every time when I step on the ice. Just help my team to win the Cup. Just playing right. Playing solid, fast, just do everything that I need to do, just do my job."
