It quoted French investigators as saying Andreas Lubitz tried a controlled descent earlier that day.
Lubitz is suspected of deliberately crashing the Airbus 320, killing all 150 people on board.
The plane had been flying from Barcelona to Duesseldorf on 24 March.
The French authorities are due to publish an interim report on the investigation later on Wednesday.
Bild quoted sources close to the investigation as saying that Lubitz tried a ?controlled, minute-long descent for which there was no aeronautical reason?.
The descent occurred on the plane?s outbound flight from Duesseldorf to Barcelona on the same day, they added, citing data on its ?black box? flight recorder.
The co-pilot is known to have suffered depression in the past.
Last month German prosecutors revealed that Lubitz had rehearsed suicide methods and the security of cockpit doors.
Voice recorder findings suggest he locked the pilot out of the cockpit on the doomed flight.