McDonald was recalled from Triple-A Sacramento on Sunday.
Double-A Richmond reinstated McDonald (groin) from its 7-day injured list Sunday.
McDonald is on the injured list at Double-A Richmond with a groin injury, Jim Callis of MLB.com reports.
McDonald was optioned to minor-league camp by the Giants on Monday, Susan Slusser of the San Francisco Chronicle reports.
The Giants added McDonald to their 40-man roster Tuesday.
McDonald (arm) was reinstated from High-A Eugene's 7-day injured list May 5 and made his season debut a day later, covering three innings and giving up one earned run on four hits and two walks while striking out three in a 4-2 win over Spokane.
McDonald is on the 7-day injured list with High-A Eugene and is building up arm strength in extended spring training, Jim Callis of MLB.com reports.