Nick Kyrgios has apologised after being fined $10,000 (£6,400) for an "insulting remark" he made to Stanislas Wawrinka during their Rogers Cup match.
On-court microphones apparently picked up Kyrgios, 20, making a lewd suggestion about Wawrinka's girlfriend.
French Open champion Wawrinka, 30, said it was "unacceptable" and called for the Australian to be punished.
"My comments were made in the heat of the moment and were unacceptable on many levels," said Kyrgios.
"In addition to the private apology I've made, I would like to make a public apology as well.
"I take full responsibility for my actions and regret what happened."
The Association of Tennis Professionals (ATP) said the fine was the "maximum on-site amount", adding it was still reviewing the matter and "additional penalties may be forthcoming".
After withdrawing from the second-round match because of injury in Montreal, Wawrinka said: "There is no need for this kind of behaviour.
"I really hope the ATP will take major action against him this time."
Speaking on court immediately after the match, world number 41 Kyrgios claimed he had been provoked by the Swiss world number five.
He said: "He was getting a bit lippy with me. Kind of in the heat of the moment, I don't know, I just said it."
Fellow Australian Mark Woodforde said Kyrgios is "behaving very poorly" and fining him was not enough.
"Perhaps in a way the financial awards have muddied the integrity and the behaviour of some of these tennis players," Woodforde told BBC Radio 5 live.
"I'm just baffled. Myself and other past Australian greats must be shaking their heads. This is not the legacy we have left.
"As an Australian I'm just bitterly disappointed that a countryman in the heat of the battle can come up with such derogatory comments towards another tennis player. It's appalling, it's uncalled for."
World number one Novak Djokovic said Kyrgios "deserved" his punishment.
Speaking after a routine 6-1 6-2 third-round win over Jack Sock, Djokovic said: "I think it is very important to keep the fairness in the sport. There is no excuse for what he has said."