Aussie Open chief urges coaching clarity after Serena row

World tennis chiefs need to clarify their position on in-match coaching to prevent another incident after Serena Williams' US Open meltdown, the head of the Australian Open said Monday.

The 23-time Grand Slam champion was warned for receiving coaching from the players' box during Saturday's final, triggering a row with the chair umpire in her 6-2, 6-4 loss to Naomi Osaka.

Williams was docked a point for smashing a racquet and she called umpire Carlos Ramos a "thief" and a "liar", an outburst for which she was sanctioned a game at a critical juncture in the second set.

Australian Open tournament director Craig Tiley said coaching, which is allowed a Women's Tennis Association events but not at men's or Grand Slam tournaments, remained a grey area.

"It all centred around coaching... the sport has to really get itself sorted out on what it does with coaching," he told reporters.

"Are we going to have coaching? Are we not going to have coaching? What is it going to look like?"