According to a No Cut News report released on March 17, Kai had sustained an injury during dance practice, resulting in a swollen ligament of his left ankle. Despite this injury, Kai will still be performing for the remainder of EXO's tour.
An SM rep informed No Cut News, "Kai will limit as much movement as possible in order to participate in the encore concert. In the case of energetic dance songs, performing normally will be difficult. After the concert is over, he will get some rest and plans to receive treatment."
Kai himself also relayed this unfortunate news to fans on the EXO-L official webpage, apologizing for something he had no control over. He said, "I feel so helpless and sad that such a thing has happened. I'm very sorry to all my fans. I'll get well quickly so I get show you a better me for the rest of the year."
No need to apologize Kai, just get the rest you need!