Earlier today Microsoft made a statement. In this statement Microsoft has made it clear they will be suspending all sales in Russia. Since Bethesda is a subsidiary of Microsoft this has trickled down to Quake. All players from Russia, and Belarus are suspended from competing in both the Quake Pro League, and Quake Challengers.
The gist of the situation is Bethesda can not in good faith allow people to participate in the Quake Pro League or Challengers if they can not guarantee their payment to them. This snippet from the Challengers Ruleset makes it clear that Sanctions from the U.S. Treasury Department can disqualify you.