The person spoke to The Associated Press on condition of anonymity because the trade has not officially been announced.
The Braves also get third baseman Chris Johnson. Atlanta is giving up four minor leaguers in the deal, including top pitching prospect Randy Delgado. The other minor-leagues headed to Arizona are right-hander Zeke Spruill, shortstop Nick Ahmed and first baseman Brandon Drury. Prado can become a free agent after this season.
Upton, who has five-plus major league seasons but still is just 25 years old, will join older brother B.J. Upton, who recently signed a free agent contract with Atlanta. The younger Upton, who has three years and $38.5 million left on his contract, had been the subject of trade speculation throughout the offseason and vetoed a trade to the Seattle Mariners.
Prado made the All-Star team in 2010 as a second baseman and played mostly in left field last season. A versatile infielder, Prado was projected to move to third base for the Braves this season to replace the retired Chipper Jones. He is expected to play third for Arizona.
Arizona had accumulated a glut of outfielders, signing Cody Ross as a free agent last month. Upton was the most marketable.
Upton, the No. 1 overall pick in the 2005 draft, raced through the minors and came up to the big-league club in August 2007 at age 19.
Upton has played five full major league seasons, so his best years could well be ahead of him. Last season, he hit .280 with 17 home runs and 67 RBI but did score a career-high 107 runs. In 2011, while helping Arizona to its surprising NL West crown, Upton hit .289, with 31 home runs and 88 RBI; the latter two categories are career bests. Overall, he's a career .278 hitter with 108 home runs.
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