“His over the board progress has been unusual, and throughout our game in the Sinquefield Cup I had the impression that he wasn’t tense or even fully concentrating on the game in critical positions, while outplaying me as black in a way I think only a handful of players can do.”

Niemann wasn’t available to remark right away.

“I have never cheated in an over-the-board game. If they want me to strip fully naked, I will do it. I don’t care. Because I know I am clean,” he said recently.

Carlsen reiterated his concerns about cheating in sports while pleading for stricter detection measures.

The Norwegian expressed worries about doping in the sport, and the International Chess Federation (FIDE) acknowledged this last week.

“Chess organizers and all those who care about the sanctity of the game we love should seriously consider increasing security measures and methods of cheat detection for over-the-board chess,” Carlsen added.

“We must do something about cheating, and for my part going forward, I don’t want to play against people that have repeatedly cheated in the past, because I don’t know what they are capable of doing in the future.”