The new administration's America-first message may damage domestic tech companies' access to foreign markets and resources, particularly in China, he said.
"Our relationship with China is going to change radically and it doesn't look like it's going to get better," McNamee said.
Most unsettling to the investor is the potential destruction of global partnerships that have been built up over the past 70 years. Trump is trying to dismantle the Trans-Pacific Partnership (TPP), an agreement between the U.S. and 11 other countries, among other trade partnerships.
"If we lose the TPP one of the levers of protecting American companies will go away," he said.
"Trump favors nationalism, which is inherently more pessimistic, and when it follows globalism inevitably it has to lead to a shrinkage in demand, and less gross domestic product around the world," McNamee added.