Kyrgios in hot water again over jaw-dropping girlfriend sledge

Controversial Australian tennis star Nick Kyrgios could be in hot water again after sledging Swiss opponent Stan Wawrinka during their second-round clash at the Montreal Masters.

In a comment picked up by a courtside microphone, Kyrgios links the reigning Australian and French Open champion with another teenaged Australian player, Thanasi Kokkinakis.

"Kokkinakis banged your girlfriend. Sorry to tell you that mate," said Kyrgios midway through the second set.

In the third and deciding set with Wawrinka 4-0 down, the Swiss retired because of a lower back injury allowing Kyrgios to win the match 6-7 (8) 6-3 4-0 to advance to the third round.

Kyrgios has already drawn the ire of Australian tennis officialdom several times already this year.

But Tennis Australia was thrilled that Lleyton Hewitt had agreed to take on a mentoring role with Kyrgios, beginning this week.

Hewitt and Kyrgios are also playing doubles together in Montreal.