James sat out the Lakers' 115-101 road loss to the Milwaukee Bucks Tuesday night due to a sore left groin. He missed over a month earlier this season because of a strain to the same groin muscle.
"We're a much better team when he's on the floor," Walton said before the Bucks game. "So I'm looking forward to him getting back out there again."
The Lakers trail the LA Clippers by 10.5 games for the eighth and final playoff spot in the Western Conference, meaning James' personal streaks of 13 straight postseason appearances and eight straight NBA Finals berths are all but finished.
James is averaging 27.5 points, 8.5 rebounds and 8.0 assists this season. He had 33 points in Sunday's 124-123 loss to the Knicks in which he had his worst shooting quarter as a pro.
Sitting out Tuesday gives James three days' rest before the Lakers' next game Friday at home against the Brooklyn Nets.
MVP front-runner and Bucks star Giannis Antetokounmpo was also ruled out of the game Tuesday with an injury.
Antetokounmpo turned his ankle and crumpled to the ground after colliding with Joel Embiid during Sunday's loss to the Philadelphia 76ers. He stayed on the ground for nearly a minute, clutching his right ankle before getting back on his feet.
He finished the game with a career-high 52 points, but he left the arena with a protective sleeve on the ankle underneath his sock.
Mike Muscala, who scored 2 points in 11 minutes, started in James' place against the Bucks.
ESPN's Malika Andrews and Dave McMenamin contributed to this report.