Seven players have been forced to pull out of Wimbledon on Wednesday in the most injury-hit second round in the competition's history.

Women's second seed Victoria Azarenka and men's sixth seed Jo-Wilfried Tsonga were among those who withdrew.

Organisers rejected Azarenka's claims that the courts were of poor quality, describing them as "excellent".

But Maria Sharapova, who lost to Michelle Larcher De Brito on court two, referred to the surface as "dangerous".

Analysis

"Players these days are more reliant than ever before on traction, especially on hard courts.

"You need to be much gentler and lighter on grass and skip over the surface. You can't be so dependent on pushing off. I think the players are trying to do the same things they do on a hard court and they can't do that on grass.

"Because the bounce is higher these days some of them think, "I'm going to play this like a hard court," and I'm just not sure you can move like that.

"Grass makes you move in a different way to clay and players use completely different muscles and a different technique."

Earlier, Steve Darcis, who beat Rafael Nadal in the first round, pulled out with a shoulder problem, while both Marin Cilic and John Isner retired with knee injuries and a left hamstring problem ended Radek Stepanek's campaign.

Yaroslava Shvedova then also withdrew ahead of her second-round match with eighth seed Petra Kvitova, citing an injury to her right arm.

"There have been no changes in the preparation of the courts and as far as we are aware the grass court surface is in excellent condition," the All England Lawn Tennis And Croquet Club (AELTC) said in a statement.

"In fact we believe that it is drier than last year when the prevailing conditions were cold and wet.

Two-time semi-finalist Azarenka fell heavily during Monday's 6-1 6-2 first-round win over Maria Joao Koehler of Portugal and required lengthy treatment before continuing with heavy strapping on her knee.

"The court was not in a very good condition that day. My opponent fell twice and I fell badly," said Azarenka.

"I don't know if it's the court or the weather. I can't figure it out.

"There is nothing I've done wrong that cost me to just withdraw from Wimbledon."

The statement from AELTC continued: "A grass court is a natural surface and will generally be slightly more lush in the first couple of days.

"Although a number of players have withdrawn injured, only one player has attributed this to slipping over on court."

Tsonga also withdrew with a knee problem while trailing Ernests Gulbis 3-6 6-3 6-3. The number six seed required treatment at the end of the second set but he failed to recover and pulled out at the end of the third.

Darcis, who was scheduled to play Lukasz Kubot of Poland, pulled out before the game could get under way.

"The injury happened against Rafa in the middle of the first set when I fell down," he said.

"A few hours after the Nadal match, I start to feel so much pain, I couldn't sleep that night.

"I saw the physio and the doctor yesterday. They did a good job. It's a little bit better today. But no chance I can play."

Injury forces Isner to retire against Mannarino

Both Isner and Stepanek required treatment during their second-round matches but also failed to recover enough to continue.

American Isner had played just two games of his match against Adrian Mannarino of France when he was forced out with an injury to his left knee.

"I always serve and land on my left leg, like I have done 20 million times playing this game, and this is the first time I just felt this sharp pain," he said.

Stepanek soon followed, trailing one set to love and 5-3 to 24th seed Jerzy Janowicz, when he retired with a hamstring problem.

Cilic made it five withdrawals when he pulled out ahead of his second-round match with Frenchman Kenny De Schepper.