The league alleged that Karl attended several workouts at Marquette University and made contact with a player not eligible for the NBA draft. The workouts were held May 16-18.
Also, the team was fined $250,000. The player was not named.
"George made an innocent mistake but we take full responsibility for these actions," said Nuggets General Manager Kiki Vandeweghe. "The Denver Nuggets fully respect league rules and regulations and we regret any inadvertent violation that occurred."