The team confirmed Tuesday that the 31-year-old veteran will remain in L.A. and is expected to be placed on injured reserve within 24 hours.
Kings officials would not confirm that Gagne is suffering from a concussion after getting "banged up" and sitting out the third period of Monday's 4-3 win over the Phoenix Coyotes.
The seven-time 20-goal scorer has a history of concussions and other injuries. He was shut down in the 2007-08 season after being diagnosed with a concussion.
The Kings take on the Blackhawks in Chicago on Wednesday and visit Winnipeg on Thursday.