In 2014, Mr. Deripaska filed a legal action in a Cayman Islands court seeking to recover his investment in Pericles, which is now defunct. He also said he had paid about $7.3 million in management fees to the fund over two years. Mr. Deripaska did not respond to requests for comment.

Mr. Manafort’s lawyer, Mr. Hibey, disputed the account of the Black Sea Cable deal contained in Mr. Deripaska’s Cayman filings, and said the Russian oligarch had overseen details of the final transaction involving the acquisition. He denied that Mr. Manafort had received management fees from Pericles during its operation, but said that one of Mr. Manafort’s partners, Rick Gates, who is also working on the Trump campaign, had received a “nominal” sum.

Court papers indicate that Pericles’ only deal involved Black Sea Cable.

Mr. Manafort continued working in Ukraine after the demise of Mr. Yanukovych’s government, helping allies of the ousted president and others form a political bloc that opposed the new pro-Western administration. Some of his aides were in Ukraine as recently as this year, and Ukrainian company records give no indication that Mr. Manafort has formally dissolved the local branch of his company, Davis Manafort International, directed by a longtime assistant, Konstantin V. Kilimnik.

At Mr. Manafort’s old office on Sofiivska Street, new tenants said they had discovered several curiosities apparently left behind, including a knee X-ray signed by Mr. Yanukovych, possibly referring to tennis matches played between Mr. Manafort and Mr. Yanukovych, who had spoken publicly of a knee ailment affecting his game.

There was another item with Mr. Yanukovych’s autograph: a piece of white paper bearing a rough sketch of Independence Square, the site of the 2014 uprising that drove him from power.