The large pane fell from Clarendon Towers into Oxford Terrace about 1pm.
"Some of the glass fell through the roof of the atrium at a local bar where a man was injured. He was treated at the scene by ambulance," Senior Sergeant Colin Campbell said.
The road was closed for several hours and the Fire Service helped clear the scene.
Police, Occupational Safety and Health and Christchurch City Council building inspectors would investigate, Mr Campbell said in a statement.