Shea, 29, has five starts as part of seven appearances in the league. He has no goals or assists.
Ambrose, 25, has two starts. He recently returned to training with the first team after a procedure was performed on his right knee. However, de Boer said Ambrose hasn’t been cleared for contact, so he can’t be selected for Sunday’s game at Sporting KC.
De Boer has also used Michael Parkhurst and Franco Escobar for short stints near the ends of games as left fullbacks. Gordon Wild, a left-footed striker who has been training as a fullback going back to last season, also is available for selection.
During the offseason, Atlanta United traded left backs Greg Garza to Cincinnati and Chris McCann to D.C. United.
Bello started two games as part of three appearances last season. His first start was because the four players ahead of him on the depth chart at left back all suffered injuries. Bello has scored one goal.
Bello is one of five Homegrown Signings on Atlanta United’s roster. The others are Andrew Carleton, Lagos Kunga, Patrick Okonkwo and Chris Goslin.
Should Bello miss three months and were to return in early August, there would be 10-11 games remaining in the regular season.
Atlanta United has a roster spot available and the trade window will remain open until Tuesday.