"Unsubstantiated reports" refers to information or claims that have not been supported or proven with evidence. It means that there is no solid proof or confirmation for the accuracy or truthfulness of the reports. Full definition
The chiefs of America's intelligence agencies last week presented Obama and President - elect Donald Trump with a summary of unsubstantiated reports that Russia had collected compromising and salacious personal information about Trump, two officials with knowledge of the briefing said. (nystateofpolitics.com)
«The evidence we took suggests that the government has at times given insufficient weight to available evidence and placed too great a reliance on unsubstantiated reports that often have their origin in the media.» (politics.co.uk)
The writer is sure that the referral will ultimately fizzle out; yes it is true that Chelsea were willing to pay a # 35 million transfer fee in August 2017 but paid only # 15 million in this January window (with unsubstantiated reports suggesting that the player's agency was paid # 7 million for their role in this slightly odd saga) and it is true that in any normal business — where an asset depreciated at a rate of # 1 million per week before it was sold — eyebrows would be raised. (thegamblingtimes.com)