Smyth, off to a sensational start this season, suffered an upper body injury during Monday night's game at Florida.
"It'll be a test for us, no doubt," Kings head coach Terry Murray told ESPN.com. "He's been an important player for us since the beginning. And with the way that line was playing with great chemistry and great things happening, it'll be a challenge for sure."
The 33-year-old Canadian Olympic hopeful had 23 points (9-14) in 22 games in his first year with the Kings while playing on the top line with NHL leading scorer Anze Kopitar and right-winger Justin Williams.
"Every team goes through it, especially this year," said Murray. "All these injuries that are happening to key players around the league, everyone is going through it and nobody is going to feel sorry for you.
"You just realize that there will be an opportunity for somebody else."
Alexander Frolov will replace Smyth on the top line.
Frolov went scoreless in 21 minutes of play against Philadelphia, managing just one shot. He hasn't scored a goal in 10 games, and has just four this season while getting bumped to the checking line.
"Frolov will get a chance, I like the way he's been playing recently," said Murray. "He ended up on that line the other night in Florida after the injury (to Smyth) and he played well with Kopy and Willy. So I'm hoping real good things happen for the line and I'm hoping Fro jumps on that opportunity."
Pierre LeBrun covers the NHL for ESPN.com. Information from The Associated Press was used in this report.