Police responded around 5:30 a.m. to an accidental injury call in the 100-block of West Jackson Boulevard in the Loop.
The 40-year-old worker told officers he tried to make room for a package that was due to arrive Tuesday morning by removing a brace from the bottom of a scaffold.
The scaffolding, which was about 15 feet up, fell on him, police said. He suffered injuries to his back and chest wall.
He was transported in serious condition to Northwestern Memorial Hospital, where his condition stabilized.
Police said Chicago's Department of Buildings and Department of Streets and Sanitation have been notified.