Serena Williams should apologise for her umpire outburst - Rugby referee Nigel Owens

Serena Williams rants at referee Brian Earley during her bad-tempered women's singles final loss at the US Open last weekend. Photo / AP

Rugby referee Nigel Owens is backing fellow official Carlos Ramos, the tennis umpire who was accused of being a 'thief' by Serena Williams in the US Open final.

Owens, rated as one of the top referees in the world, weighed in on the Serena Williams outburst in a column for the Wales Online.

"It is the nature of the beast that sports stars will be unhappy with referees from time to time, particularly when they have lost a game. But if they have real grievances, there are proper guidelines and procedures to follow. Calling someone a 'thief' and accusing him of sexism, in front of millions across the world, is not the right way to go about it and even more wrong when there are no grounds for it, Owens wrote.

Owens said the tennis star should apologise for her actions in the defeat to Naomi Osaka. The Welsh referee said it has happened often to him in rugby where a player has disagreed with him but said referee's don't hold grudges with players.

"Serena is a role model for tennis, for black people, also for women in sport, and she would be better served accepting she got this wrong, apologising for her behaviour and the accusations she threw at the umpire.

"[She] has put Carlos Ramos in a really awkward position for next time he umpires one of her games, or one involving some of her colleagues who have come forward in support of her.

"However, I've no doubts he will continue to act with dignity and integrity. He won't hold grudges, but at the same time nor will he want to edge towards her with a bit of favouritism, which would lead to other accusations."

"In calling Ramos a 'thief', and accusing him of sexism, Serena was in effect calling a highly respected official a cheat. One, by the way, who has no history for that sort of thing and who has handled matches, men and women, perfectly fairly and with integrity," Owens said.

"Ramos has a reputation of being a ridiculously strict umpire, in men's and women's tennis, so the accusation of sexism is difficult to understand."

Williams' return to the court remains unknown with a chance she may take the rest of the tennis season off.