Real Madrid says Kaka has reinjured his left knee and will be out two weeks.
He will miss a La Liga match against Hercules on Saturday and the return leg match against Lyon in the Champions League.
Kaka, who also has been hampered by a groin injury, reported pain in his knee following a match against Deportivo La Coruna on February 26, and hadn't returned since.
Real Madrid have won both La Liga matches without him, outscoring their opponents 10-1.
