O'Neal posted a video on Sunday on his Instagram account, showing Howard's appearance on MTV's Wild 'N Out. In the video, Howard gets dissed for not playing in 2004 and Howard's history of switching teams.
"Dam," O'Neal wrote for the caption on the post, which had more than 1.8 million views as of Monday morning. The post also had thousands of comments, including a few from Howard.
"Shaq, we can have a roast battle if you want," Howard wrote. "I got 10 in the chamber for you lol."
"I only battle champions lil man," O'Neal replied. "You ain't in my division. You're in Charles Barkley's division. Focus on getting that ring brother."
O'Neal, 46, was inducted into the Naismith Memorial Basketball Hall of Fame in 2016. The 15-time All-Star and 1999-00 MVP won four NBA titles, three with the Los Angeles Lakers and another with the Miami Heat, before calling it quits after the 2010-11 season.
Howard is playing for his sixth different NBA franchise after signing with the Wizards in July. The 32-year-old was the No. 1 overall pick in the 2004 NBA Draft. Howard is an eight-time All-Star, but has only reached the NBA Finals once during his decorated NBA tenure. He helped the Orlando Magic to a 59-23 record in the 2008-09 season, ending with a 4-1 series loss to the Lakers in the championship.