Rivers said O'Neal was placed back in the immobilizing boot as a measure to help speed up his recovery by reducing the inflammation that occurred when he tried to ramp up his activity last week.
"I don't know if it's precautionary, because he's always been injured," said Rivers. "I just think [Boston's training staff is] trying to speed it up, more than it is getting worse. Honestly, I don't get involved in it. I just know they decided to do it, to put a boot on it."
"I don't think it's a setback because ... we haven't really set a date when he was coming back. Talking to [team trainer] Eddie [Lacerte] again, he still thinks it's around a week or so. I've been saying a week now for three weeks, but I don't think it's changed any."
The Celtics remain optimistic that O'Neal, who has been sidelined with the injury since Feb. 1, could return next week.
O'Neal traveled with the team on a recently completed three-game road trip with the goal of participating in walk-through activities as he ramped up toward game action. But the foot that has been prone to flare-ups did so again, forcing the team to aggressively attack with the injection, which sources said happened on Tuesday.
A source told ESPN Boston on Wednesday that O'Neal would hopefully be back on the floor by April 1, allowing him two weeks before the end of the regular season to shake off rust and get acclimated with his teammates again.
At Wednesday's practice, assistant coaches Kevin Eastman and Armond Hill, who handled media chores as coach Doc Rivers gave himself a day off from reporters, said they had no further update on O'Neal's condition.
"We haven't [heard anything further]," Eastman said, suggesting Rivers might know more Friday. "But you have to win in spite of, not lose because of -- does that make sense? You win in spite of what's going on with your team. You don't say, 'Well, we're not winning because of it.' As a coaching staff, we're telling our players, whatever predicament is thrown at us, we just have to deal with it and fight our way through it. Figure it out rather than use it as an excuse. You can't advance if you live off of excuses."
But can the Celtics win a world title without Shaq?
"I think we need everybody," admitted Hill. "We need Jermaine [O'Neal]. We need everybody. We need them on the floor, in practice, at walk-through. We can't eliminate anything."
Rivers also acknowledged Friday that Jermaine O'Neal (left knee surgery) will rejoin the team Monday in Indiana then engage in his first team basketball activities during an off-day practice on Wednesday in San Antonio.
Rivers also said Von Wafer will not play Friday against Charlotte or Sunday in Minnesota, but there's a chance he will join the Celtics on the upcoming four-game road trip given his speedy return to the practice court Thursday. But Rivers stressed that he still believes Wafer is a ways out from game activity.
Chris Forsberg covers the Celtics for ESPNBoston.com.