It was the seventh full game O'Neal missed this season. Alonzo Mourning started at center for Miami in its 80-72 loss to the Pistons, his first start for the Heat since April 17, 2002.
"He's feeling a lot better, but it's not prudent to put him out there and subject his body to that kind of stress right now," Heat coach Stan Van Gundy said of O'Neal.
Van Gundy said O'Neal would play in Miami's next game, Thursday at Philadelphia.
Mourning finished with 10 points, a season-high 14 rebounds and five blocked shots -- but struggled from the field, shooting 3-for-12.
"Defensively, he was great. His effort was fantastic. He's awarrior. Plays as hard as he can," Van Gundy said. "Offensively, obviously, he had a major struggle."
O'Neal, who was at the arena for Sunday's game and said he also expects to return this week, lost 12 to 15 pounds because of the virus, Van Gundy said. Team physicians examined O'Neal on Saturday and advised the coaching staff to err on the cautious side.
"He's starting to eat. He's up and around. His energy level is starting to come back up," Van Gundy said. "We're confident that he'll be fine for later in the week. Would have loved to have had him today, obviously, in a game like this, but at the same time, you want to be smart."
The Heat are 4-3 without O'Neal in the lineup this season.
Miami already has clinched the No. 1 seed for the Eastern Conference playoffs, but is hardly playing an inconsequential string of games to end the season. The Heat are 1½ games behind Phoenix in the race for the NBA's best record, and entered Sunday tied with San Antonio for the league's second-best mark.
"If we were in a situation where in this game, we could win it and that would assure us the best record, Shaq wouldn't play," Van Gundy said. "He's not ready to go."
O'Neal is averaging 23 points a game this season. He's fifth in the league in rebounding (10.6), sixth in blocks (2.4) and leads
the NBA in field-goal percentage (.599).
Mourning has averaged 4.0 points in 10.9 minutes in 14 games since rejoining the Heat earlier this season. He played in 18
games, starting 14, for the New Jersey Nets, who traded him to Toronto in the deal for Vince Carter. But Mourning never reported to the Raptors, who bought out his contract and made him a free agent.