Kopitar sustained a right knee injury in a game on Saturday, playing for Mora in Sweden.
ESPN reported that Kings GM Dean Lombardi said Kopitar is expected to miss three weeks.
Kopitar's agent, Pat Brisson, told the Los Angeles Times the Slovenian star will have tests on the injured right knee, but noted "it's nothing to be alarmed with."
It's not known how many games Kopitar could miss. The NHL and the players' association reached a tentative agreement on a new labour deal on Sunday, paving the way for the regular season to start, but a start date has not yet been determined.
Kopitar had 25 goals and 51 assists (76 points) in 82 regular-season games for the Kings last season. He tied for the playoff lead with 20 points as the Kings won their first Stanley Cup.