The person spoke on condition of anonymity because the deal had not been announced.
Ross, who turns 32 Sunday, adds to the abundance of outfielders on the Arizona roster, leading to speculation a trade may be ahead. He .267 with 22 home runs and 81 RBIs last season with the Boston Red Sox. He's a career .267 hitter in nine big league seasons.
The addition gives the Diamondbacks four veteran outfielders -- Ross, Justin Upton, Gerardo Parra and Jason Kubel -- along with two youngsters the organization has deemed ready for the majors -- Adam Eaton and A.J. Pollock.
That would indicate a trade could be in the works with Kubel the center of that speculation. In his one season with Arizona, the left-handed slugger hit .253 with 30 home runs and 90 RBIs. He was hitting .300 on July 22 but batted .176 with 19 RBIs the rest of the season.
Ross, who throws left-handed and bats right-handed, was a fourth-round draft pick of Detroit out of Carlsbad, N.M., High School in 1999. He had brief major league stints with the Tigers, Los Angeles Dodgers and Cincinnati before becoming a full-time big leaguer with the Florida Marlins. Ross was claimed by San Francisco off waivers in August 2010 and was MVP of that year's NL championship series, when he hit .350 with three home runs in five RBIs against Philadelphia. He also homered against Texas in the World Series.
He committed one error in each of the last two seasons.