Kings general manager Rob Blake announced his star power forward's injury Thursday.
Carter was hurt on a hit by Jeff Petry during the Kings' 5-1 victory over Montreal on Wednesday night to extend the best start in franchise history (5-0-1). Petry's skate came off the ice and connected with the inside of Carter's lower leg during the first period.
Carter has three assists in six games this season for the Kings, who start a six-game road trip Saturday in Columbus.
Carter had 32 goals and 34 assists last year in his highest-scoring season since 2011. His absence will strain Los Angeles' depth at center behind captain Anze Kopitar.
Forbort became a regular on the Kings' blue line last year during his first full NHL season, contributing 18 points while playing in all 82 games. The Kings' first-round pick in 2010 was eighth in the NHL in ice time among rookies with more than 20 minutes per game.
Laich is a 12-year NHL veteran who went to training camp with the Kings on a professional tryout contract. He was released shortly before the season began, but kept practicing with Los Angeles.
The 34-year-old Laich has scored 331 points in 764 career games with Washington, Toronto and Ottawa. He appeared in 27 games last season with the AHL's Toronto Marlies, but didn't give up on his desire to return to the NHL.