Mattek-Sands' husband Justin Sands tended to her as she lay on the turf of court 17, but it was almost 20 minutes before medical staffers removed her via a stretcher to a waiting ambulance, the New York Post reported.
The 32-year-old's right knee seemed to give way as she played a shot in the third set of the match on Court 17 against Sorana Cirstea.
Her opponent Sorana Cirstea rushed to her side but she could hardly look as she saw the American's knee "out of place".
Safarova went to the court on learning of the injury sustained by her doubles partner and close friend.
She added: "She kept staying, Sorana help me, Sorana help me, Sorana help me".
Mattek-Sands, a wildcard entry to the singles, is a doubles specialist and in tandem with Lucie Safarova has won the last three grand slam titles, at the US Open, Australian Open and French Open. She was later seen in tears courtside.
Short Says Repealing Obamacare With Later Replacement an Option
Rate this article Do you want to leave a comment? Trump subsequently anointed McConnell's Senate version as much better and more humane.
The WTA tweeted about the incident: 'It is an acute knee injury and she has gone straight to hospital'.
"It was heartbreaking because she went into shock and it took a while until the medical team was there ..." In this kind of moment when she was screaming so loud, you watch the knee, it was a very uncomfortable moment.
The screams coming from Wimbledon's Court 17 were bone-chilling.
To the casual tennis fan, Mattek-Sands is nearly certainly best known for her dress sense.
The Sun reported Mattek-Sands' comments as she was taken off the field.