As head of the National Assembly, Guaido proclaimed himself acting president in January 2019 after the legislature declared Maduro a "usurper" who was re-elected through fraud.
Trump was speaking one day before the Senate will vote on whether to remove him from office for pressuring Ukraine to dig up dirt on a political rival.
On Tuesday, the Venezuelan opposition leader was a special guest at Trump's State of the Union address, during which the USA president introduced him as a bastion against socialism.
The White House said the two presidents are working to expedite a democratic transition and end the economic crisis in Venezuela.
Trump took aim at the Venezuelan government in his yearly address in Washington, DC, claiming that Maduro's "grip of tyranny will be smashed and broken".
He was quickly recognized by more than 50 countries, including the United States.
But Guaido's efforts to oust Maduro through street protests have fizzled and USA sanctions have failed to move the leftist leader, who still enjoys the support of his military as well as Russian Federation and China.
Streatham attack: police shoot man dead after 'terror related' stabbing
London Mayor Sadiq Khan said he was aware of the situation and had contact with the Metropolitan Police and local representatives. He thanked emergency services for their response. "My thoughts are with the injured and all those affected", he added.
"Mr. President, please take this message back to your homeland", Trump said to Guaidó.
Trump's public embrace of Guaido suggests the president still sees him as the best chance to replace Maduro, despite scepticism he's voiced in recent months to aides.
In Caracas, Maduro called on the "honest sectors" in the United States to halt Trump's "interventionist, illegal and immoral" policies that are leading to a "high level conflict" against Venezuela.
During a press conference after the meeting Wednesday, Trump officials told reporters, "Any harm that may be caused on Juan Guaidó on his return to Venezuela will have very significant consequences".
Foreign minister of Venezuela Jorge Arreaza called US President Donald Trump an "arrogant charlatan" and denounced the "interventionist rhetoric" in his State of the Union speech.
Guaido is recognized by the USA - and several other countries - and the interim president of Venezuela, even after his unsuccessful efforts to overthrow Nicolas Maduro's regime.
"He'd be sitting in the president's palace, or at least waging a fight to win".