|Wimbledon 2017 on the BBC|
|Venue: All England Club Dates: 3-16 July Starts: 11:30 BST|
|Live: Coverage across BBC TV, BBC Radio and BBC Sport website with further coverage on Red Button, Connected TVs and app. Click for full times.|
Bethanie Mattek-Sands retired from her second-round Wimbledon singles match after collapsing on court with what appeared to be a serious knee injury.
The American slipped during the third set against Sorana Cirstea on court 17 and screamed in agony.
The 32-year-old was given lengthy medical treatment by paramedics before being carried off on a stretcher and taken straight to hospital.
She could be heard screaming "please help me, please, please".
Mattek-Sands was also due to compete in the women's doubles competition, where she and partner Lucie Safarova were bidding for their fourth consecutive Grand Slam title.
Safarova arrived on court in tears and Mattek-Sands was also comforted by her husband Justin.
Romania's Cirstea said: "I freaked out. I have never seen such an injury before, the knee was really in a bad position. It was like something you see only in the movies.
"I tried to comfort her but I panicked. I felt useless. All she kept saying was 'Sorana, help me, help me'.
"I wish I could have done more. You wouldn't wish that on your worst enemy."
Cirstea also questioned the speed of the medical response to the injury saying her opponent spent "too long on the ground".
"I turned around and told them to bring a stretcher or something," Cirstea said. "I think everyone froze. No-one was having any reaction.
"She went into shock. It took a while until the medical team was there. I think for a long time it was me, her husband and my physio.
"I don't know for how long she was on the ground, but I would say 10, 15 minutes.
"There are sports where you see something's happening and you see the help straight away - like football, boxing, all the others.
"Here it took a while, so of course you wonder what would happen if it was a heart issue or something."
In response, the All England Club said: "The first response to court 17 was within one minute by a qualified ambulance technician.
"The player was kept on court while pain relief was given. The player was then transferred directly to an ambulance and taken under emergency conditions to a hospital."
BBC tennis correspondent Russell Fuller
It is a real shock to the system to see a tennis player lying on a grass court surrounded by oxygen and stretchers.
It is sadly a more familiar sight in contact sports like rugby and football, but not at Wimbledon, where in the relatively quiet surrounds of court 17, Mattek-Sands' anguish could be all too clearly heard.
The timing is so cruel for the 32 year-old as she and her doubles partner Lucie Safarova had the chance to hold all four Grand Slam titles simultaneously by winning at Wimbledon.
Safarova was also in some distress at the side of the court, as she arrived to comfort her friend before heading out to play singles against Shelby Rogers.
Former Wimbledon finalist Sabine Lisicki: Omg no no no This is so heartbreaking
World number 21 Daria Gavrilova: I know the feeling.... stay strong
Women's doubles Grand Slam champion Sara Errani: I have no words... be strong I send all my energy to you