The Organization for Economic Cooperation and Development (OECD) on Tuesday said German GDP is likely to grow 0.4 percent this year and 1.9 percent next year.
According to the report, the slowdown was due to slowing investments and consumption spending.
The OECD warned that there would be unusually high levels of uncertainty and considerable risks is the business world this year.
On a positive note, German banks remained highly leveraged as reforms in the banking system started taking effect.
The OECD also projected that German GDP growth may fall below 1 percent at the beginning of the next decade.
"This primarily reflects a decline in potential employment by around 0.5 percent a year over the period 2016 to 2025 as the German population ages," said the report.