The Heat fined Whiteside an undisclosed amount Sunday for "comments detrimental to the team" following Miami's 110-109 overtime loss to the Brooklyn Nets on Saturday. Whiteside had questioned the Heat's decision to match the Nets when they went to a small lineup when "we've got one of the best centers in the league."
"It's behind us," Spoelstra said Monday, according to the South Florida Sun-Sentinel. "You can tell right now by the mood of the gym that's long gone. The only reason we're addressing out of obligation to all of you because it really is a team matter, a family matter. We're focused on getting the next one and securing our spot in this dance."
Spoelstra did note he was disappointed that Whiteside chose to make his displeasure public rather than handling it as a team, calling it "poor timing" and "poor judgment."
"Guys want to throw a few eggs after the game or T.P. my house, that's actually a better way to deal with it than speaking to [the media] about the frustrations," Spoelstra said.
Whiteside didn't play in the final 21 minutes Saturday -- the last four of the third quarter then all of the fourth quarter and overtime -- after both teams went small.
"A lot of teams don't have a good center," Whiteside said. "They are going to use their strengths. It's bulls---. It's really bulls---, man. There are a lot of teams that can use a center."
Whiteside on Monday chalked up his expletive-filled rant to frustration.
"I was just frustrated, man," Whiteside said. "I was frustrated that we lost. I really wanted to get that game. ... I could have handled it different. But I got so caught up in wanting to get that win. I get real competitive. I really want to be out there. But I just trust coach's decision."
Whiteside, who has missed 29 games this season because of injury, has seen his playing time average decrease to 25 minutes per game in 2017-18, down from 29.1 minutes in 2016-17, when he finished as the league's leading rebounder. The previous two seasons, he averaged 32.6 minutes.
Saturday's game was the second for Whiteside in his return to the court after missing the previous nine games with a hip injury. He said he was pleased with how he felt after Monday's practice.
"I feel great," Whiteside said. "We had a great practice. I'll leave it up to the coaching staff's hands."
Spoelstra insisted that Whiteside's role was not in question.
"It has nothing to do with the role," the Heat coach said. "He knows exactly what's expected of him as he continues to get back in shape. He knows what I want out of him and what his teammates want out of him. He'll continue to work to get back in shape, and we'll get him back to where he was before he got hurt about three and a half weeks ago."
The Heat can clinch their 20th playoff spot in 30 seasons with a win over the Atlanta Hawks on Tuesday.
If healthy, on the floor and in form, Whiteside will play a significant role for the Heat in a playoff run.
"He can help us a lot," Dwyane Wade said. "Obviously he's got to continue to get in game shape like all of us that come back from injuries because you've got to get confident in your body, so that takes a little while, but when he's into it, he's one of the most dominant centers in the game."
The Associated Press contributed to this report.