updated 5:41 p.m. ET Jan. 21, 2010

CLEVELAND - Cavaliers starting point guard Mo Williams will miss at least one month with a sprained left shoulder, a major blow to the Eastern Conference’s top team.

Williams injured his shoulder in Tuesday night’s win over Toronto when he reached for a steal in the third quarter. He was taken to the locker room for an examination and treatment before returning to the floor and making a key 3-pointer in the fourth quarter.

The Cavs said Thursday before their game against the Los Angeles Lakers that an MRI taken at the Cleveland Clinic revealed the sprain and that Williams is projected to be out for the “next four to six weeks.”

On Tuesday, the Cavs initially said Williams had sustained a strain, but changed the diagnosis to a sprain, which indicates there is a tear in the shoulder. It is not yet known if surgery is an option for Williams, the club’s second-leading scorer behind LeBron James.

Williams, who was an All-Star last season — his first with Cleveland — scored a team-high 28 points in the Cavaliers’ Christmas Day win over the Lakers.

Cleveland coach Mike Brown said Delonte West, who is more of a shooting guard, will start in place of Williams and that Daniel Gibson will return to the rotation after having his minutes reduced in recent weeks. West will be making his first start this season.

“It’s tough,” Brown said. “But I like the guys in this locker room and I’m confident other guys will step up. It’s part of the business. You hope he gets better soon, but you have to keep going forward.”

Losing Williams will hurt the Cavs in a variety of ways. Other than James, he is the club’s best offensive playmaker and is one of the NBA’s best three-throw (90 percent) and 3-point shooters (43 percent).

Cleveland (32-11) entered Thursday’s game against the Lakers with a 3½-game lead over Boston for the East’s best record.

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