Howard batted just .184 with one extra-base hit in 42 plate appearances in 11 games for Triple-A Gwinnett. The 37-year-old also struck out 11 times.
Atlanta signed Howard last month in a bid to see if the former Philadelphia Phillies slugger had anything left in the tank.
Howard spent 13 seasons with the Phillies before the club used a $10 million buyout on his contract in the off-season. He shared the team lead in homers with 25 last season but also batted a career-worst .196.
Howard enjoyed his best season in the City of Brotherly Love in 2006, when he set career highs in homers (58), RBIs (149) and batting average (.313) en route to being named the National League Most Valuable Player.
Howard also set the tone in the 2008 World Series, launching three homers as Philadelphia dispatched the Tampa Bay Rays in five games.
His 382 homers rank second on the Phillies' career list, behind Hall of Famer Mike Schmidt. Howard has also collected 1,194 RBIs and batted .258 with Philadelphia.
Howard hit 30 or more homers and drove in more than 100 runs in six straight seasons from 2006 to 2011.