Boston big man Daniel Theis was also ruled out because of an illness.
Walker was hospitalized after sustaining a neck sprain Friday when he collided with Ojeleye during a game against the Nuggets in Denver.
Walker had been listed as doubtful, which was surprising given how serious the injury looked on Friday. He remained on the floor for several minutes after the collision. Play was stopped as medical personnel from both teams tended to him. He left the court on a stretcher.
Celtics team doctor Tony Schena met with reporters Monday to explain Walker's treatment.
"Luckily Kemba has done very well," Schena said.
The team initially said the star guard had concussion-like symptoms, so he went through concussion protocol.
"When he landed, he had numbness and tingling in his hands," Schena said. "He never lost consciousness, and he stayed on the floor mostly as a medical precaution."
The doctor said Walker had spine and neck imaging in Denver that showed no significant structural damage, and then Walker passed a full cervical spine evaluation Saturday in Boston.
Walked also had a full cognitive review on Saturday and passed that. On Sunday, he woke up with no symptoms, then went to the team facility and had further neurological testing. He passed without any issue, so he had a light workout.
All that is left to complete the concussion protocol, Schena said, is for Walker to participate in a practice, which will be Tuesday.
"He's been good, and he feels good," Celtics 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.