MILAN: Female models provocatively revealed the letters A or B when they were picked by the male tennis players. One model pulled up her dress to reveal an A on her thigh.
The draw ceremony for the Next Gen Finals was supposed to highlight Milan's status in the fashion industry.
Instead, the ATP was accused of being sexist.
Two-time Grand Slam champion Amelie Mauresmo tweeted, "Disgrace," and Andy Murray's mother, Judy, added, "Awful."
A day after the ceremony, the ATP and tournament sponsor Red Bull apologized on Monday.
"In no way was this meant to be offensive to anyone," ATP executive chairman and president Chris Kermode said at a prescheduled news conference for the tournament. "The intention was to mix the heritage of Milan, of fashion. Unfortunately, the execution was unacceptable. We apologize and I can assure it won't happen again."
Kermode refused to allow the players to answer any questions on the issue.
"We take full responsibility for what happened," he said. "We put them (the players) out there and we apologize. In no way was it anything to do with the players here."
ATP and Red Bull also released a brief statement a few hours before the news conference.
"The intention was to integrate Milan's rich heritage as one of the fashion capitals of the world," they said in the statement. "However, our execution of the proceedings was in poor taste and unacceptable. We deeply regret this and will ensure that there is no repeat of anything like it in the future."
The Italian tennis federation declined comment, saying the ATP organized the draw ceremony.
It is not the first time tennis has been embroiled in a sexism row. At the 2015 Australian Open, Serena Williams and Eugenie Bouchard were asked to do a twirl by an on-court TV interviewer after their victories.
The Next Gen Finals starting on Tuesday in Milan features the top seven 21-and-under players in the rankings plus one Italian wild card. The top seeds are Andrey Rublev and Karen Khachanov.
Top qualifier Alexander Zverev withdrew to focus on the elite ATP Finals next week in London.
Rublev, Denis Shapovalov, Chung Hyeon and Gianluigi Quinzi were drawn in Group A. Group B features Khachanov, Borna Coric, Jared Donaldson and Daniil Medvedev.