Bethanie Mattek-Sands was left screaming in agony after suffering an "acute knee injury" in a horrific fall during her second-round match against Sorana Cirstea at Wimbledon.

The match was locked at one set each when Mattek-Sands' right leg buckled in the opening game of the decider as she approached the net.

Mattek-Sands, who has endured a spate of injuries through her career, immediately clutched her knee and the American was heard screaming "please help me" in disturbing scenes.

Cirstea hopped the net to try and aid her stricken opponent, as the umpire called for paramedics.

Mattek-Sands received medical attention on Court 17, while her doubles partner Lucie Safarova arrived and was in tears as she offered comfort before the American was stretchered away and taken to hospital in an ambulance.

Mattek-Sands, ranked number one in the WTA doubles standings, and Safarova were bidding to complete a non-calendar Grand Slam in the women's draw.