The initial fear is that Cousins has a torn ACL, but nothing is expected to be known for certain until he undergoes further tests in Los Angeles on Thursday, sources told ESPN.
Cousins, a four-time All-Star, is expected to meet with Lakers team physicians, sources said.
Cousins, 29, was working out in Las Vegas on Monday when he had to leave the court after what one source described as "bumping knees" with another player.
Cousins, who has averaged 21.2 points and 10.9 rebounds over his nine NBA seasons, signed a one-year, $3.5 million contract with the Lakers in July. He's part of a Lakers team expected to be among the NBA's elite this season.