Pageau was recalled from AHL Binghamton last Sunday due to an injury to Zack Smith. He has now been pencilled in as Lazar's replacement.
"I said it's a win-win," Senators coach Dave Cameron said Thursday. "What it's going to do is give us a real good look at (Pageau). We think he's a guy in the organization that's done a lot of good in the American Hockey League. He was sent down after he was cut, which I'm sure was a major disappointment.
"We think he's an NHL player so it's going to open up an opportunity for him to show what he can do and we feel that he can come in and provide the same role that Curtis was doing."
Pageau, who has played in 38 career NHL games, was most impressive during the Senators' playoff run in 2013 when he scored a hat trick in a first-round game against the Montreal Canadiens.
He played 28 games last season but didn't make the cut out of training camp this season. Senators general manager Bryan Murray said sending Pageau to Binghamton was one of the toughest decisions the organization had to make.
The 22-year-old was clearly disappointed, but worked hard in the minors and had 18 points (8-10) in 25 games.
Pageau just smiled when asked whether he or Lazar was happier about the world junior loan.
"I think we're both happy," he said.
"For me it's a good thing, it opens up a spot for me for a couple of games," Pageau added. "I don't know how long I was supposed to be here or what's going on with me, but for sure it's opened up a chance for me and an opportunity and I'll do my best to help the team and for sure I wish him the best."
Cameron admitted that with injuries to Smith and Chris Neil, the decision to release Lazar was difficult. However, knowing that Pageau was available to fill the void helped.
The head coach added that if Pageau hadn't been playing so well in Binghamton there was a good chance Lazar wouldn't be going to the world juniors.
"I think that's fair to say, especially with the injury to Smitty," he said. "Now you start thinking a little deeper because you're down one less guy. You're still one less guy in terms of depth because of Smith's injury so it's a little more intense for the coach. I've always said ... I don't make decisions based on fear of injuries. If they're going to happen, they're going to happen."
Cameron is confident Pageau will fill in nicely for Lazar.
"I think Pageau can match that, based on his play," he said. "I'll have to answer that after Pageau plays some games, but (I'm) very confident he can come in and provide us with that."
After taking five of a possible six points on their recent road trip, the Senators are looking for a strong finish before the Christmas break. Ottawa has a tough task ahead with three games in four nights starting Friday against the visiting Anaheim Ducks.
"This past road trip wasn't pretty, but if you told me at the beginning we'd be coming home with five out of six points, I'd be pretty happy," said forward Kyle Turris. "There's obviously lots of stuff we have to improve and work on, but we're moving in the right direction.
"The pace of our game I think has come up quite a bit."