Blue Jays GM Ross Atkins said Thursday that Bieber (elbow) will throw off a mound this week, Keegan Matheson of MLB.com reports.
The right-hander has been limited to throwing on flat ground while working his way back from shoulder fatigue, so a return to mound work is a significant development in his rehab program. Bieber still has a lengthy road ahead of him while building up to face live batters and eventually embarking on a rehab assignment, but a return in early May still appears to be on the table.