McDonald was placed on the 15-day disabled list on July 2, retroactive to June 25, nursing a slight strain of his left oblique, which he thought was suffered in Kansas City in mid-May.
The 37-year-old shortstop took some swings in batting practice Sunday, a step D-backs manager Kirk Gibson had been keeping a close eye on.
"He's back at our spring facility, and he's getting better," Gibson said. "He's starting to kind of let it go and that's what he was waiting for."
McDonald is batting .267 this season with four home runs and 12 RBIs.
Gibson said he hopes to have McDonald back in the lineup soon after the four-game Cincinnati series.
"Hopefully, by the end of the week, he can start playing games," Gibson said.
Shortstop Stephen Drew, who recently returned to the lineup, is hitting .205 with eight hits and three RBIs in 39 at-bats this season entering Monday.