Shenzhen - US Open champion Bianca Andreescu withdrew from the season-ending WTA Finals on Thursday due to a knee injury.
The Canadian sensation crashed out of contention at the round-robin tournament when she retired hurt against Karolina Pliskova on Wednesday. Andreescu injured her left knee in the third game after attempting to return a wide serve and received heavy strapping during the subsequent medical timeout.
The 19-year-old gamely fought on but was noticeably hobbled and retired after the first set, which Pliskova won 6-3 in 51 minutes.
Andreescu had lost her opener against Simona Halep in a three-set thriller on her WTA Finals debut.
"I had a scan Thursday to check my knee after last night's match, and unfortunately the results show that I need to withdraw," she said.
"On the spot the physio thought it was my meniscus, so she taped it up. It was really hard to bend with the taping and the pain kept getting worse, so I had to stop," she added.
During a breakout season, which she started ranked 178, Andreescu compiled a remarkable 48-7 record and won her first Grand Slam after defeating Serena Williams in the final at Flushing Meadows.
"I'm definitely going to take time off, recoup and then start my pre-season," she said.
"I'll become even stronger for 2020."
World No 12 Sofia Kenin will replace Andreescu for Friday's dead-rubber against defending champion Elina Svitolina, who has already clinched top position from the Purple Group.
Kenin will be the second replacement used at the tournament after Kiki Bertens stepped in for world number three Naomi Osaka, who withdrew due to a shoulder injury.