Winterkorn told the company's annual news and analyst conference that "Volkswagen is feeling the headwinds especially in Europe."
However, he said he was "guardedly confident" and that this year's operating earnings should match last year's. In 2012, VW recorded record sales and earnings.
Winterkorn said prospects were better in the United States, "where the upward trend is continuing," and in China. He said that of 10 planned new plants, seven were in China, strengthening future earnings there.
Volkswagen is doing better than Europe's other mass-market carmakers, who are struggling with fierce competition and slumping demand in southern Europe due to the debt crisis that has seen unemployment rise, especially among the young people who are a key market for smaller, cheaper cars.
Volkswagen's flagship brand has done well while its luxury brands, such as Audi and Porsche, are enjoying higher profits per vehicle.