Julian Assange's extradition hearing is due to begin at London's Old Bailey on Monday.
The four-week hearing is expected to hear claims that the Wikileaks founder was placed under covert surveillance by a company linked to US President Donald Trump’s biggest financial backer.
Assange claims cameras were placed around the Ecuadorean embassy in central London, where he was living as a fugitive, by US security services, The Times reported.
Assange, 49, is in the high-security Belmarsh prison in south London as he fights an extradition request by the US to stand trial there on espionage charges.
He faces charges under the US Espionage Act for the 2010 release by WikiLeaks of a trove of secret files detailing aspects of US military campaigns in Afghanistan and Iraq.
A ruling against Assange could land him in jail for 175 years.
He is accused of working with former US soldier and whistle-blower Chelsea Manning to get classified documents from databases containing about 90,000 Afghanistan war-related activity reports, 400,000 Iraq war-related reports and 250,000 State Department documents.
Assange took refuge in the Ecuadorean embassy in London in 2012 after skipping bail to avoid separate legal proceedings in Sweden, but was dragged out by British police last year.
The allegations of the US spying on him are expected to be at the heart of his case to avoid extradition to the US.
Assange claims he will not receive a fair trial if he is extradited.
He was allegedly placed under surveillance by Undercover Global, a company based in Spain that had been hired by the Ecuadorean government in 2015 to protect him at the embassy.
The Times reported the company's owner, David Morales, was recruited at a trade fair in Las Vegas.
At the fair he also received a contract from Sheldon Adelson, the chief executive of Las Vegas Sands, a US casino and resort company, which has donated more than $200 million (Dh734.6m) to Mr Trump’s campaigns, to provide protection for his superyacht.
Mr Morales is being investigated in Spain over the alleged London surveillance.