TUI declined to comment on the matter, the newspaper said.
Last week, Mordashov raised his stake in the company to just above 10 percent from five percent and said he planned to launch a joint venture with TUI on the Russian market.
Major shareholders are gearing up for a much-anticipated general assembly on May 7 and the latest development boosts TUI boss Michael Frenzel, who counts Mordachov as an ally.
The Russian investor has replaced Norwegian shipping magnate John Fredriksen as the largest TUI shareholder, though Fredriksen reportedly wants to increase his 5.12 percent stake and gain a seat on the group's supervisory board.
Frenzel was forced by a group of shareholders led by Fredriksen to separate the maritime shipping activities from the rest of the group