Serena Williams has been spared a potentially explosive reunion with the lineswoman whose foot-fault call against her in the US Open semi-final last month provoked the most controversial outburst of the tennis year.

Although the unnamed Japanese woman, whose identity has remained a closely guarded secret within the sport, will not be a part of the officiating team at the season-ending Sony Ericsson WTA Tour Championships, which start in Doha on October 27, the reasons for her absence remain the subject of heated conjecture.

The umpiring fraternity, which holds the lineswoman in high regard, believes that she was told not to travel to the Middle East because of the possible drama her presence might provoke, while the WTA insisted last night that she had been invited to attend and declined for family reasons.

Whatever the truth, she would have been considered for a place among the officials who will participate in the $4.5 million eight-player finale of the women’s season. The Times understands that her marks during this year’s US Open Series — the American lead-up events to the Open and the final grand slam of the year itself — placed her among the highest echelon of those dedicated amateurs who travel the world calling lines.

While the Qatar tennis federation selects the umpires for the championships, the decision on who to nominate as linespersons rests with the women’s tour. The WTA said that while it was “brought to our attention that she [the lineswoman] would be travelling to Doha”, it is absolutely insistent that she turned down an invitation to participate.

This new twist happens while those charged with determining the final outcome of an investigation into the Wimbledon champion’s outburst in the semi-final against Kim Clijsters, of Belgium, have taken more than a month to deliberate and are still to reach a decision. The tipping point came when Williams was called for a second-serve foot fault at 15-30, when trailing 6-4, 6-5. Her subsequent rant contained at least four expletives and the threat that she would, if she could, “shove this f***ing ball down your f***ing throat and kill you.” As the score had become 15-40, and Williams had already been warned for breaking the frame of her racket in an earlier incident, the point penalty awarded for her outburst handed the Belgian her place in the final.

Williams later said: “I want to sincerely apologise first to the lineswoman, the United States Tennis Association and mostly tennis fans everywhere for my inappropriate outburst. I’m a woman of great pride, faith and integrity, and I admit when I’m wrong.

“I need to make it clear to all young people that I handled myself inappropriately and it’s not the way to act — win or lose, good call or bad call, in any sport, in any manner. I like to lead by example. We all learn from experiences both good and bad, I will learn and grow from this and be a better person as a result.”

In the meantime, the investigation drags on and on. It has been deemed a “major offence”, the ITF has received reports from the lineswoman, umpire, tournament referee and WTA Tour supervisor. Bill Babcock, the ITF grand-slam administrator has to determine whether the initial $10,500 (about £6,600) fine handed to Williams for her on-court misdemeanours is enough of a punishment.

Babcock’s recommendation will go to chairmen of the four grand-slam events for verification. Williams, 28, would have leave to appeal to an independent tribunal should she not agree with their verdict.

Clijsters, who returned to the circuit after a two-year absence to start a family in August and won the US Open in her third tournament back, is celebrating again. Last night, her sister, Elke, a former Wimbledon junior doubles champion, gave birth to a son, Cruz Leo, the second name after their father, who died in January.