The Boston Celtics officially ruled out guard Kemba Walker for Monday night's home game against the Sacramento Kings.

Boston big man Daniel Theis was also ruled out due to an illness.

Coach Brad Stevens declined to say who would start in Walker's place.

Walker was hospitalized after suffering a neck sprain Friday when he collided with teammate Semi Ojeleye during a game with the Nuggets in Denver.

Walker had been listed as doubtful, which was surprising given how serious the injury looked on Friday night.

He is expected to go through a full practice Tuesday.

"Luckily Kemba has done very well," Celtics team doctor Tony Schenna said.

Schenna met with reporters Monday to explain Walker's treatment. The team initially said the star guard had concussion-like symptoms, but he was never diagnosed with a concussion, Schenna said.

"When he landed, he had numbness and tingling in his hands," Schenna said. "He never lost consciousness and he stayed on the floor mostly as a medical precaution."

Schenna said Walker passed concussion tests in Denver on Friday night, and the next day in Boston.

Walker remained on the floor for several minutes after the collision with Ojeleye. Play was stopped as medical personnel from both teams tended to him.

A brace was placed around Walker's neck to stabilize the area, and he was strapped to a backboard before being placed onto a gurney and wheeled off the court.

"He's been good, and he feels good," coach Brad Stevens said Sunday. "It's kind of a minor miracle based on what we saw the other day. But the strain is real, and he's got some soreness in his back and neck. That's it."

Walker had played in 158 consecutive games before Monday

ESPN's Tim Bontemps contributed to this report.