Upton joined the likes of Matt Kemp, Wil Myers and Derek Norris in moving to the Padres in December, as Atlanta and San Diego agreed to a six-man trade.
The Padres sent infielders Dustin Peterson and Jace Peterson, plus outfielder Mallex Smith and left-handed pitcher Max Fried to Atlanta, receiving Upton and right-armer Aaron Northcraft in return.
Upton is entering the final year of his contract and will be paid $14.5million in 2015, before becoming eligible for free agency at the end of the season.
The 27-year-old hit 29 home runs for the Braves last term and had 102 RBIs to his name to earn a Silver Slugger award in the MLB's National League.