World Snooker has spoken to referee Terry Camilleri about Ronnie O'Sullivan using chalk to line up a shot at the World Championship.
O'Sullivan, 39, placed the chalk on the table but was not reprimanded for breaking the rules during Tuesday's quarter-final against Stuart Bingham.
Camilleri was asked for his interpretation of the incident and the matter has been resolved.
There is no possibility of any penalty for O'Sullivan, who trails 5-3.
"The referee is unaware, Ronnie is too but for me, that is a foul. You are not allowed to do that," said BBC Sport pundit Ken Doherty.
Although O'Sullivan was allowed to finish his break in the fifth frame, he went on to lose the next three as Bingham opened up a 5-3 lead after the first session.
The match resumes on Wednesday at 14:30 BST.
Camilleri should have called a foul when O'Sullivan placed his chalk on the table to line up a shot, as snooker rules state a seven-point penalty will be awarded to the opponent if a player 'uses any object to measure gaps or distance'.
Doherty added: "As far as I am aware, you are not allowed to put the chalk on the table because you are using it as a tool to measure the ball.
"That is exactly what Ronnie has done. Stuart Bingham was looking at him and should really be aware. If he had more knowledge of the rules, he would have jumped up out of his chair."
It is not O'Sullivan's first controversial moment at the Crucible in this championship.
He escaped a fine after briefly playing in his socks in his first-round win over qualifier Craig Steadman. He also came close to snapping his cue during his second-round match against Matthew Stevens.
In 2013, 'The Rocket' was warned by referee Michaela Tabb for what she believed was an improper gesture during his semi-final against Judd Trump.
Regarding O'Sullivan's latest incident, Tabb - who resigned from the tour in March - said on Twitter: "Chalkgate...Foul seven. I don't have Terry's opinion though, he may have seen it differently. Also the Crucible is the hardest venue to ref in."