Government sources said a special ED team conducted searches at his Gurgaon premises and seized a number of digital and other documents.
Sources said Raj, who runs a number of hotels including one in Switzerland, was later brought to the ED office and questioned for several hours.
They said his questioning revolved around certain transactions conducted by him worth several lakh dollars. Sources said he recorded his statement.
His statement included details about his association with Khan and his business dealings in the country and in foreign countries. The ED has asked him to be available for further questioning.
The ED is probing Khan for allegedly amassing massive wealth through money laundering and tax evasion.
Khan was earlier detained by the ED which carried out multi-city searches at his Pune home and his associates'premises cracking the whip to meet tomorrow's Supreme Court deadline.