Bynam has a torn MCL, an MRI showed Monday. He'll be out for 8-12 weeks.
Bynum, who was coming into his own during his fourth NBA season and averaging 26.2 points and 13.8 rebounds in his previous five games, hurt his knee in the first quarter Saturday at Memphis after teammate Kobe Bryant crashed into his right leg.
The 21-year-old, 7-footer didn't return, but X-rays were negative. The MRI wasn't.
"Everybody's just upset for him and disappointed for him," said Bryant of Bynum, who missed the final 46 games last season after bruising a bone in his knee and briefly dislocating his kneecap. Bryant made his comments before knowing the outcome of the MRI.
Now, without Bynum for possibly the rest of the regular season, Los Angeles (37-9) must turn its focus to New York (21-25), which has won six of its last seven games. The Knicks, though, open a brutal stretch that includes visits from Eastern Conference powers Cleveland on Wednesday and Boston on Friday.
The Lakers are trying for their third straight victory on a six-game road trip.
"We've got a huge test with three teams coming in here that we're going to need to get a couple victories, and I think we've got a chance to do it," said forward David Lee of the Knicks, who are one half-game back of Milwaukee for the final playoff spot in the East.
First up are the Lakers, who have won six of their last seven overall and the last three meetings with the Knicks.
Bryant scored 25 points and Pau Gasol added 24 and eight rebounds Saturday against his former team.
Bryant had 28 points in a 116-114 home win over New York on Dec. 16 and is averaging 30.5 on 49.5 percent shooting in his last four games versus the Knicks. He had 39, 11 rebounds and eight assists in his last visit to MSG, where the Lakers won 95-90 on Dec. 23, 2007.
Los Angeles, though, is facing a much improved New York team that's looking for a fourth straight victory overall and sixth in a row at home.
Al Harrington scored 31 points and Lee added 23 with 17 rebounds in New York's 122-113 win at Indiana on Saturday. The Knicks shot 48.9 percent in moving within two wins of matching their total from last season.
"I'm pleased with the way we're playing and the group we have because they're really trying," first-year Knicks coach Mike D'Antoni said. "We won't look back, we'll look forward. We want to make the playoffs, we've said that all along."
Harrington is helping them do that, averaging 20.5 points and 6.3 rebounds in 33 games since joining the Knicks and their up-tempo offense after being traded from Golden State.
"This is the perfect style of play for me," said Harrington, who is averaging 14.5 points in 19 games versus the Lakers. "I'm having a lot of fun and I haven't had fun in a while."
Lee, an All-Star snub, is averaging 20.2 points and 14.3 rebounds in his last six contests.
Nate Robinson had a season-high 33 points for the Knicks in the December loss at Los Angeles.
Information from STATS LLC is included in this report