But he was able to enter the country in another way during that period, according to previously undisclosed court documents. Mr. Deripaska came to the United States eight times between 2011 and 2014 with government permission as a Russian diplomat, according to affidavits he gave in a little-noticed lawsuit in a Manhattan court. Mr. Deripaska said in the court papers that his visits were brief and made in connection with meetings of the G-20 and the United Nations, not to conduct business.

The court documents and public records show that Mr. Deripaska, whose companies have long had offices in New York, has expanded his American holdings over the past 10 years, buying high-priced Manhattan townhouses and a major stake in a Russian-language newspaper in New York.

The lawsuit was brought by Alexander Gliklad, a Russian-born businessman, who charged that Mr. Deripaska had used his diplomatic status as a cover to do business, which the oligarch denied. Mr. Gliklad claims he is entitled to collect funds that Mr. Deripaska had agreed to pay to settle a lawsuit with a man who owed Mr. Gliklad money from a court judgment. Last month, a New York State Supreme Court justice rejected Mr. Gliklad’s argument that the Manhattan court had jurisdiction over Mr. Deripaska.

As Mr. Manafort’s dealings with Russia-friendly Ukrainian politicians, business activities and loans have come under examination in recent months, his former client has gotten caught up in the media scrutiny. The two men were partners in an offshore fund set up in 2007 to buy telecommunications and cable television assets in Ukraine, where Mr. Manafort had advised then-President Viktor F. Yanukovych. That deal fell apart, winding up in litigation in the Cayman Islands.