Boston Bruins forward Shawn Thornton on Monday appealed his 15-game suspension for attacking and injuring Pittsburgh Penguins defenseman Brooks Orpik on Dec. 7, according to the NHLPA and Thornton's agent.
The next step for Thornton will be an appeal hearing with commissioner Gary Bettman, which has been scheduled for Friday morning, a source told ESPN.com's Pierre LeBrun.
If the suspension remains six or more games after Bettman makes a ruling, Thornton can then appeal to an independent arbitrator.
Thornton participated in the Bruins' practice Monday morning.
The NHL's department of player safety handed down its suspension on Saturday after Thornton had his in-person disciplinary hearing Friday at the league's office in New York.
Thornton did not travel with the team on its four-game trip.
"We felt for him being home and not with us," forward Patrice Bergeron said. "He's a great team guy, a veteran leader on our team, so we definitely miss him."
Other teammates voiced their support for Thornton after Monday's practice, as well.
"It's about trying to be there for him. Obviously, he's a friend and a teammate," Bergeron said. "He obviously regrets what happened and would probably like to take that moment back. But that being said, he's living with the consequences and we all need to do that, also, and respect the league's decision."
Orpik suffered a concussion and was removed from the game on a stretcher. He remains out.
Information from ESPN.com's Pierre LeBrun was used in this report.