Mateo (elbow) is set to begin a minor-league rehab assignment at Triple-A Norfolk on Tuesday, MLB.com reports.
Mateo is entering the final stages of his recovery from left elbow inflammation. The 30-year-old speedster has a chance to rejoin Baltimore's roster before the end of June, but he should be able to return in early July at the latest. Mateo primarily served as a pinch runner and defensive specialist prior to going down, having slashed .180/.231/.279 with one home run, three doubles, three RBI and 14 stolen bases over 65 plate appearances.