South Africa's Kevin Anderson.

Johannesburg – Top South African tennis player Kevin Anderson has suffered a costly setback in his first comeback tournament after undergoing elbow surgery following this year's Australian Open.

Anderson, the defending champion, on Friday night lost 6-2 7-6 (1) to top American player John Isner in the quarter-finals of the Delray Beach Open – reversing the result which the South African had achieved on the way to winning his second ATP title last year.

The defeat has serious consequences for the 29th world-ranked Anderson, who is set to shed close to 200 points next week and slip down the rankings by as many as six or seven positions after equalling a career-high 28th position earlier this year.

The 26 year-old Anderson had displayed some of the most impressive form of his career while accounting for Isner and Andy Roddick at Delray Beach last year, but this time Isner gained a comprehensive revenge and powered his way to an impressive victory while serving no fewer than 16 aces and dominating the second-set tiebreaker.

The South African had also struggled to beat Yen-Hsun Li in three sets in the previous round when there was a distinct rustiness to his play.

Anderson, however, might well point to the fact that this was his first tournament in more than a month since reaching the fourth round of the Australian Open and going down to world number six Tomas Berdych in four closely-contested sets.

Meanwhile, while all the other candidates have made themselves available for South Africa's Euro-Africa Davis Cup tie against Poland in April, Anderson is still sitting on the fence and is non-commital about participating in the crucial tie in Warsaw.

South African Davis Cup captain John-Laffnie de Jager was due to announce his squad two weeks ago, but there has been a delay while Anderson decides whether or not to play.

De Jager said South African Tennis Association CEO Ian Smith was currently involved in negotiations with Anderson and hoping to come up with a deal that will persuade South Africa's top player to play.

“With the Poles boasting a player of the calibre of the world's 26th-ranked Jerzy Janowicz and a strong, all-round supporting line-up,” added De Jager, “our hopes of qualifying for a fifth successive World Group play-off later in the year would depend heavily on Kevin's presence - and I'm holding thumbs he sees fit to represent his country on this important occasion.”

Victory would give South Africa a further play-off tilt at returning to the elite World Group of the Davis Cup in 2014 after an absence of almost 14 years.

In the past four years, South Africa have failed to break the elsuive barrier at the final hurdle after suffering frustrating defeats against India, Germany, Croatia and Canada in turn. – Sapa