(Adds more injuries)
By Sonia Oxley and Neil Maidment
LONDON, June 26 (Reuters) - Second seed Victoria Azarenka called on Wimbledon organisers to examine the state of the grass courts after joining a growing list of players to withdraw from the grand slam because of injury on Wednesday.
The Belarussian fell badly in her match on Monday on what she called a slippery Court One and her knee failed to recover in time for Wednesday's second-round clash with Flavia Pennetta.
Azarenka was one of seven players to withdraw from the championship on an incident-packed third day at the tournament.
"I don't know if it's the court or the weather. I can't figure it out it," said the second seed, who joined John Isner, Marin Cilic, Radek Stepanek, Steve Darcis, Jo-Wilfried Tsonga and Yaraslava Shvedova in withdrawing.
Croat Cilic described the trauma as a "very black day".
The sorry seven represent the most singles retirements on the same day at a grand slam in the Open Era, and took the total tally to 10 after Guido Pella, Philipp Kohlschreiber and Romina Oprandi cut short their campaigns on Tuesday.
"It would be great if the (All England) club or somebody who takes care of the court just would examine or try to find an issue so that wouldn't happen," Azarenka added.
Russia's Maria Sharapova was another player taking spectacular tumbles on the court and out of the championships when she lost to powerful Portuguese qualifier Michelle Larcher de Brito.
The four-times grand slam champion fell three times on a slippery Court Two, something Sharapova said she could not recall doing in a match before, although she refused to blame her second-round exit on the surface.
It is the first edition of the tournament since the retirement of long-time head groundsman Eddie Seaward but a Wimbledon spokesman insisted there was nothing different about the courts this year.
"The surfaces at the start (of the tournament) are always lusher than at the end," he said. "We have not changed the way the courts have been prepared or watered."
Most of the other players injured on Wednesday had not picked up their problems slipping on the courts, with sixth seed Tsonga, one of the day's high-profile casualties, succumbing to a problematic knee tendon that forced him to retire early while trailing Latvia's Ernests Gulbis.
American Isner and Cilic also pulled out with knee injuries while Belgium's Darcis, who stunned Rafa Nadal in the first round, had a shoulder problem and Czech Stepanek had left hamstring trouble. Kazakh Shvedova withdrew with an arm injury.
Many players, including Britain's world number two Andy Murray, told reporters the courts felt the same as in any other year, while Cilic also struggled to find a reason for it.
"(It's a) very black day ... it's difficult to say what the explanation is," the 10th seed, who said he had felt some pain in his knees for much of the grasscourt season, told a news conference.
While Darcis sustained his shoulder injury after falling in the first set of his match against twice champion Nadal on Monday, Cilic did not actually take a tumble.
"It's more because of obviously much lower bounces, putting more pressure on my body and my knees, as I'm pretty tall," the Croatian said. "It also has a difficulty on movement. It's a bit tougher to move on grass than other surfaces."
The courts had unsettled some on Tuesday, though.
Argentine Pella was carried off on a stretcher after a nasty fall and Switzerland's Oprandi was also injured. German Kohlschreiber put his retirement in the fifth set of his first-round match down to tiredness.
Azarenka, who lay on the ground screaming in agony on Monday after almost doing the splits behind the baseline, played for most of the second set of her first match in obvious pain and with her knee heavily strapped.
Asked if she thought the courts were different to past years, she replied: "I'm wondering the same question because the court was not in a very good condition that day (Monday).
"I mean, my opponent fell twice; I fell badly; there were some other people who fell after." (Editing by Ken Ferris)