Mattek-Sands lay screaming on the court after injuring her knee against Romanian Sorana Cirstea on Thursday and was carried off court and taken to hospital.
"I ruptured my patellar tendon, and I’m going to be needing surgery, so I'll be out for a while," the 32-year-old told her fans in a Facebook Live chat.
Mattek-Sands said that she had heard a "pop" in her leg as she stepped towards the net.
The American, who suffered a serious ligament injury to the same knee four years ago, has won five grand slam doubles titles with Lucie Safarova and the pair would have held all four at the same time had they clinched a sixth at Wimbledon.
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Her Czech doubles partner was reduced to tears at courtside during the incident and led a flood of messages of support for Mattek-Sands on social media.
"All your messages have been really inspiring and have meant a lot to me. The support has been amazing. I’ll get through this," Mattek-Sands said.
(Reporting by Simon Evans; editing by Clare Lovell)
