"He got tangled up with Mikko," head coach Jared Bednar said after practice. "He actually fell on top of Mikko, but his leg got trapped underneath Mikko and he fell awkwardly."
While Zadorov's status is a tough blow for the club, the Avalanche appears closer to getting two other players back in the mix.
Forward Rene Bourque (head) and blueliner Erik Johnson (broken leg) both participated in practice for the first time since each was sidelined due to injury.
"I think it's fun for them, for sure," Rantanen said. "I was injured in training camp. The first practice with the team, it's amazing when you're there with the boys and you're having fun. So that's good. It's good to see EJ back and Bourqie is coming back. It's good to see those guys.
"Everybody knows EJ is one of the best defensemen in the league, so he brings us good 'D' and power play, too--more capability there. And I think Bourqie works hard. He's a good teammate. He's a good player, too. So I think they both bring us another level."
Donning exquisite, red practice sweaters which declared them as non-contact participants, Bourque and Johnson ran through all the activities with their teammates, working up a sweat and reacquainting themselves with the tempo and structure of the daily rigors of the sport.
Johnson has missed 34 games while recovering from a broken leg suffered on Dec. 6 after blocking a shot by Dallas Stars forward Tyler Seguin.
"Today, he joined practice, did the better part of practice in an off-colored jersey," Bednar said of No. 6. "So he's improving and we'll just see what tomorrow brings. He's had some days where he's felt real good and others not. Seems to be on the right path, and hopefully he'll be joining the team for full practice here in the next few days."
His return will bolster Colorado's defensive core, especially with Zadorov's situation.
"Yeah, it's great. It's cool seeing EJ out there again. We lose him, we were a .500 team. We were a playoff bubble team, especially in the West this year," center Nathan MacKinnon said. "So we lose him and then we kind of fall off. That's how important he is to our team. When we have a guy like that playing 28 minutes a night, you know it hurts. It really hurts. Obviously, seeing him practice, you see why he's so good. There's no room out there, he's going 1-on-1 against guys and guys don't have a sniff that are really good players. So it's great seeing him."
Bourque has been out since leaving the game against the Los Angeles Kings on Feb. 1.
"He joined the non-contact stuff today, and that's the first step of the process," Bednar said of No. 17. "He'll have to go back and get reevaluated too and then see what comes up within the next couple days as well."
The Avalanche's leading scorer at one point this year, Bourque's return will add an additional scoring threat to the lineup.
"Obviously with Bourqie, he's got nine, 10 goals this year," MacKinnon said. "Hopefully we get him back soon for some depth.
"Guys have been out that are getting healthy. It's important we get those guys back. A healthy team is usually a winning team. We were a good team when EJ got hurt. We haven't been good, but we'd be better with him, for sure. It's nice to see them."
This story was updated on Feb. 20, 2017 at 5:25 p.m. MT