The man, who has not yet been caught, reportedly entered a bank on Wednesday in Higuera de Vargas, near Badajoz, and used what is believed to be a "fake gun" to intimidate an employee, according to newspaper Las Provincias.
After securing €5,000, the man fled the scene on his bicycle, but lost more than half of his booty, which was then found by another man living nearby.
The Spanish Civil Guard have launched a search for the culprit of the crime.
Local newspaper El Periodico Extramadura said that the man has been described as having a "powerful physique".
The employee who he encountered had been alone at the time and is being treated for an anxiety attack.