Jackson, 29, is a .271 career hitter with 52 home runs over stops with the D-backs, Red Sox and A's in seven seasons. But as general manager Ken Williams pointed out, Jackson never really fully recovered from Valley Fever that hit him in 2009.
"He was on a career trajectory where his ceiling was through the roof," said Williams of Jackson, who had three productive seasons in Arizona from 2006-08. "He got Valley Fever, which was a terrible thing to catch. He will be working his way back in Triple-A."