Kudlow, who is 70 years old, had just joined the Trump administration in March.
White House economic adviser Larry Kudlow gives a press briefing about upcoming G7 in the White House in Washington, US.
Trump tweeted just minutes before his historic meeting with North Korean leader Kim Jong Un that Kudlow is being treated at Walter Reed Medical Center.
"He really kind of stabbed us in the back", Kudlow said of Trudeau.
France, Germany slam Trump's G7 statement U-turn
At the G-7 summit, Trump's spokeswoman, Sarah Huckabee Sanders, said the US was "close to a deal" on NAFTA. She said: "We won't let ourselves be ripped off again and again".
The White House didn't immediately comment on his condition.
During internal White House deliberations this spring, Mr. Kudlow argued in favour of cutting a quick deal with Canada and Mexico to resolve NAFTA renegotiations, said sources with knowledge of the confidential talks.
Kudlow, a veteran CNBC anchor and commentator, was brought in largely because of his close relationship with Trump, and because of his visible comfort on television speaking about the value of the low-tax, high-growth proposals that Trump and Republicans have pushed. He did several media interviews on Sunday to vigorously defend Trump after the president's trade spat with summit host Canadian Prime Minister Justin Trudeau.