The NHL Players' Association filed the appeal Sunday night on Kadri's behalf. The first appeal goes to NHL commissioner Gary Bettman, and Kadri could then take his case to a neutral arbitrator if he so chooses.
Without Kadri, the Avalanche completed a four-game sweep of the Blues on Sunday in St. Louis. A convincing 5-2 victory over the 2019 Stanley Cup champions will give Colorado some downtime while Vegas and Minnesota conclude their series.
"I thought we got a little better as the series went along," Colorado coach Jared Bednar said. "It was a full 60-minute effort. The first three games we had some lapses in our game, some things that I didn't like. Tonight, I liked a lot."
Kadri was suspended indefinitely after injuring Faulk in Game 2, pending a video hearing with the league's department of player safety. That department handed down an eight-game suspension Friday night that rules out Kadri for the remainder of the first round and part of the second.
It's Kadri's third playoff suspension over the past six postseasons. He was suspended for the remainder of the first round in 2019 for cross-checking, which turned out to be five games, and was suspended three games for boarding in 2018.
Each of those incidents happened with Toronto, which traded him to Colorado in the summer of 2019. Kadri had 18 points for the Avalanche in the 2020 bubble playoffs when he was able to stay out of trouble.
Kadri had 32 points in 56 games this season as Colorado won the Presidents' Trophy and home-ice advantage throughout the playoffs. He traditionally occupies a spot on the team's second line.
On Sunday, Colorado flexed its depth up front -- with or without Kadri -- as Brandon Saad, Gabriel Landeskog, Mikko Rantanen, Nathan MacKinnon and Valeri Nichushkin scored as the Blues were eliminated on home ice. Philipp Grubauer made 18 saves to win his fourth game of the postseason.
"To come in here in a tough building to play and take two in a row against a desperate team, it's not easy to do," Landeskog said. "I'm happy that we got it done without giving them any sort of momentum."
The Avalanche scored 20 goals in the sweep.
The Associated Press contributed to this report.