McMahon (thumb) will begin a rehab assignment with Double-A Somerset on Saturday, Gary Phillips of the New York Daily News reports.
Manager Aaron Boone explained that McMahon will "probably" play in just one game before rejoining the Yankees, with the plan being to activate the infielder when rosters expand Sept. 1. The 31-year-old McMahon has mostly struggled at the dish in the years since he left Colorado, though his defense at the hot corner is still valuable enough to project him for a semi-regular role upon his return to the active roster.