"We will be in the red in 2013 and 2014," Steve Girsky told Focus magazine in an interview. "In 2014, hopefully a bit less. Balanced books will only be achieved in 2015 or 2016, depending on the market situation," he added.
GM's European operations have run up billions of dollars in losses over the past 10 years. It had planned to sell Opel at one stage but pulled back when it could not find a suitable buyer.
Battered by a declining European car market, Opel announced in December that it would halt auto production at its Bochum plant in 2016 but pledged to keep the site running as a parts distribution centre.
Opel employs 37,400 people in Europe, including 20,300 at four sites in Germany, in Rüsselsheim, Bochum, Eisenach and Kaiserslautern.
Opel boss Thomas Sedran told the magazine: "We do not plan further site closures."
Last week he insisted that "Opel was not for sale" amid rumours of a tie-up between the German firm and struggling French group PSA Peugeot Citroen.