Tennis authorities have opened an investigation following allegations that Australian player Bernard Tomic's father John was involved in an altercation with his son's hitting partner Thomas Drouet in Madrid.
The ATP has confirmed that an incident took place but did not give any more details.
A spokesman told Press Association Sport: "We can confirm that there was an incident and we are gathering information."
Tennis Australia said it was working with the ATP.
"Obviously media reports regarding a recent incident are very concerning," it said in a statement.
"We are working closely with ATP officials who are investigating the incident and are unable to comment further until the full facts are known."
Bernard Tomic, 20, was beaten 6-3 6-2 by Radek Stepanek in his first round-match at the Mutua Madrid Open yesterday morning as the Czech veteran set up a second-round clash with second seed and defending champion Roger Federer.