The 24-year-old suffered the injury while playing for Atlanta United's USL team on July 25. Ambrose has made nine appearances for Atlanta in MLS regular season play this season, eight starts, and has posted two assists. With Greg Garza also out longterm, the left back job in Atlanta will fall to Chris McCann. The Irishman has started the last four games at the position under Tata Martino. 16-year-old George Bello also appeared on the bench on Saturday against Toronto FC.