Andy Roddick withdrew from the season-ending ATP World Tour Finals because of a left knee injury and was replaced by Robin Soderling.
The No. 6-ranked Roddick qualified for the elite tournament for the seventh consecutive year but injured his left knee at the Shanghai Masters last month and has not competed since.
“I am really disappointed,” Roddick said. “I love playing in London and I’ve heard so many good things about the venue. However, I have not fully recovered from my knee injury and I won’t be able to compete.
“One of my goals in 2010 will be to qualify for this event again.”
Soderling, No. 9 in the rankings, was the first reserve for the eight-man field. He will be the first Swede to play at the season finale since former Australian Open champion Thomas Johansson in 2002.
The French Open runner-up will join Roger Federer, Rafael Nadal, Novak Djokovic, Andy Murray, Juan Martin del Potro, Nikolay Davydenko and Fernando Verdasco at O2 Arena for the event starting on Sunday.