An MRI on Tuesday morning confirmed the tear, according to the Warriors, who said it would provide updates on Cousins "as appropriate."
Cousins' noncontact injury occurred while he was pursuing a loose ball with 8:30 remaining in the first quarter of Monday's 135-131 loss to the LA Clippers in Game 2 of their playoff series.
He knocked away a pass from Clippers forward Danilo Gallinari. AsCousins tried to chase down the ball, he fell to the floor. He tried to get up and keep going, but once he rose to his feet, he immediately called to be taken out of the game. He then gingerly made his way back to the Warriors' locker room with team medical personnel.
Cousins returned in January after missing almost a full year of play with a torn left Achilles tendon suffered last season, when he played for New Orleans. He signed a one-year deal with the Warriors, expecting that a healthy return to play would catapult him back into the free-agent market this summer.
Game 3 of the series, which is tied 1-1, is Thursday night in Los Angeles.
"I know it's frustrating for him. I've been through something like that, getting hurt, getting all the way back and then getting hurt again, so I know how frustrating it is," Warriors center Kevon Looney said. "He is a resilient guy. He's been through adversity before and I know he's going to bounce back. His spirit is probably low right now, but he's a tough guy and he'll be back better than ever."
Looney picked up more minutes with Cousins' injury and scored a career-high 19 points Monday while making all six of his shots in 19 minutes. Kerr is likely to use a combination of shot-blocking presence Andrew Bogut and Looney going forward this postseason.
Bogut's signing last month for a second stint with the franchise means so much more now. Warriors coach Steve Kerr called him an "insurance policy" and Bogut -- who had been playing back home in Australia -- has made the most of his chances. He had nine rebounds, three points and a blocked shot in 16 minutes Monday.
He played on the Warriors' 2015 championship team and the 73-win team the following season that lost in Game 7 of the NBA Finals to LeBron James and the Cavaliers.
The No. 1 overall draft pick in 2005 out of Utah, Bogut has been open to any role Kerr chooses for him, which now could be starting.
"Obviously, there will be more minutes," he said after the game. "It'll still be matchup dependent, but I anticipate probably starting games, playing the first three or four minutes and then coming out."
Stephen Curry expects the backups to fill the void as the Warriors' depth has done all season, with Jordan Bell also likely to be in the mix.
"Exactly what they've been doing. They've been playing amazing the last part of the regular season and these first two games," Curry said. "... It may look a little different considering the skill and talent and level that Boogie can bring when he's healthy."
The Associated Press contributed to this report.
McGrady: Cousins a 'devastating loss' for Warriors
Rachel Nichols and Tracy McGrady react to DeMarcus Cousins suffering a torn left quadriceps during the Warriors' Game 2 loss to the Clippers.
Jefferson: Cousins' injury puts Warriors in a 'difficult spot'
Richard Jefferson and Jalen Rose evaluate the significance of DeMarcus Cousins' injury, both agreeing it makes the Warriors much more vulnerable.