NEW YORK -- NHL teams continue to clear salary cap space with free agency starting later this week.

The Detroit Red Wings placed forward Justin Abdelkader on unconditional waivers Tuesday for the purpose of buying out his contract. The Montreal Canadiens did the same with defenseman Karl Alzner, who had been relegated to the minors for much of last season.

Abdelkader had three years remaining on his contract at a salary cap hit of $4.25 million. His buyout will span six years for Detroit.

Alzner's buyout is four years since he had two years left at a $4.625 million cap hit.

Pittsburgh Penguins defenseman Jack Johnson cleared unconditional waivers, allowing the team to buy out the remainder of his contract. Johnson's buyout will also last six years since he had three years left on his contract.

Once they clear, Abdelkader and Alzner will join Johnson, New York Rangers goaltender Henrik Lundqvist, Arizona Coyotes winger Michael Grabner and Ottawa Senators winger Bobby Ryan as players bought out this offseason. They immediately become free agents.

The free-agent market opens at noon ET Friday. The salary cap remains flat at $81.5 million for at least the 2020-21 and 2021-22 seasons.