"The European Union stands ready to react swiftly and appropriately in case our exports are affected by any restrictive trade measures from the United States," European Commission spokesman Margaritis Schinas told reporters.
Trump told Britain's ITV channel that the EU has treated the US "very unfairly when it came to trade" and that his many problems with Brussels could "morph into something very big".
In reaction to the Trump interview, Schinas said: "For us, trade policy is not a zero-sum game, it is not about winners and losers. We here in the European Union believe that trade can and should be win-win."
Schinas added: "We also believe that while trade has to be open and fair it has also to be rules based."
Trump delivered the warning during a wide-ranging interview last Thursday on the sidelines of the World Economic Forum in Davos, where he took his "America First" agenda to the global business elite.
In a speech Friday he told the forum that his mantra "does not mean America alone" and hinted that the US could rejoin the Trans-Pacific Partnership, a deal he withdrew from a year ago.