Roman Abramovich is said to have suffered suspected "chemical weapons" poisoning alongside Ukrainian peace negotiators earlier this month.
Abramovich is said to have travelled between Moscow and Kyiv during several rounds of negotiations following Russia's invasion of Ukraine.
The Wall Street Journal report that billionaire Abramovich and at least two senior members of the Ukrainian team developed symptoms like red eyes, constant and painful tearing, and peeling skin on their faces and hands. Abramovich is also said to have lost his sight for several hours and was treated in Turkey.
Investigative website Bellingcat also tweeted: "Bellingcat can confirm that three members of the delegation attending the peace talks between Ukraine and Russia on the night of 3 to 4 March 2022 experienced symptoms consistent with poisoning with chemical weapons.
"One of victims was Russian entrepreneur Roman Abramovich."
Rustem Umerov, a Ukrainian politician, is also thought to be among those infected. There was no word from the Kremlin on the reported poisoning attempt.
Abramovich has been sanctioned by the United Kingdom government due to his links with Russian president Vladimir Putin.
He is looking to sell Chelsea, which he has owned since June 2003, and there is a deadline for the preferred bidders who want to buy the club.
Four parties have made a final shortlist to take the Blues and the Raine Group, a New York merchant basked tasked with handling the sale, have set a deadline of 11 April for the bidders to submit their final proposals.