Washington's new starting center missed all of training camp and the exhibition schedule. He did not participate in any practices until Monday.
At Washington's media day last month, Howard said his soreness resulted from traveling to China for offseason promotional appearances and called it "just a minor setback."
Ian Mahinmi replaced Howard in the lineup but played only 12 minutes, scoring 3 points on 1-of-2 shooting. Kelly Olynyk's putback of Dwyane Wade's missed jumper produced the go-ahead basket for Miami with 0.2 seconds left.
"He's getting close," Brooks said about Howard, who did not miss a single game because of injury last season with the Charlotte Hornets.
The center played in 81 of 82 games for Charlotte, missing one because of suspension.
On Thursday, Howard went out to the court pregame and took shots.
"We just don't feel like he's quite there yet. Like I said a few weeks ago, we're in no rush. We just want to make sure that he's comfortable -- we're comfortable -- going forward," Brooks said. "He's definitely going to miss tonight and, going forward, we don't know."
Washington's next game is at home against the Toronto Raptors on Saturday.
The Wizards traded away starting center Marcin Gortat to the Los Angeles Clippers and added Howard, who'll turn 33 in December, on a two-year, $11 million contract with a player option. He averaged 16.6 points and 12.5 rebounds last season and is now with his fourth team in four years.
The 6-foot-11 Howard is entering his 15th NBA season.
"We're just trying to find ways and opportunities to challenge him and push him," Brooks said. "We just need to keep giving him conditioning."