The suspension is accompanied by a referral to the league's program for Substance Abuse and Behavioral Health for evaluation and possible treatment. The league said it would have no further comment.
The Knights said the franchise respects the league's decision.
''Needless to say, we're extremely disappointed in the result, but we are very supportive of the program,'' Knights President George McPhee said after the team's morning skate. ''Zykov knowingly took supplements, tested positive and has been suspended and we support the suspension.''
In a statement, Zykov said he would work during the suspension to ensure he would be ready to contribute when he returns.
''While I haven't been able to discover how I tested positive, I understand that I am responsible for what is in my body and will accept this penalty,'' Zykov said in the statement. ''I want to apologize to my family, my teammates, and the Golden Knights organization and fans.''
Zykov, whose nameplate and gear were gone from his locker at the team's practice facility Thursday, is in his second season with the Knights. He was claimed on waivers by the Knights in December and spent the offseason in Las Vegas working on his conditioning to make the roster.
The 24-year-old Zykov is the second Knights player to be suspended due to a positive test for a performance-enhancing substance. Defenseman Nate Schmidt was suspended 20 games prior to the start of last season.
McPhee, who said the team was informed Wednesday of Zykov's positive test, called the Zykov and Schmidt cases ''completely different circumstances.''
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