Mohamed Badawy al-Husseiny, the former head of Ipic's Aabar subsidiary, is also named as a suspect in the Swiss letter. Both he and Mr Qubaisi were named in a court case launched by US authorities last month concerning a plot to misappropriate more than $1 billion of 1MDB funds, although neither man was named as a defendant. Mr Husseiny could not be reached for comment.
Mr Qubaisi abruptly left Ipic in April 2015 and his whereabouts and status since have been the subject of much speculation. He has been under investigation in Abu Dhabi for months, according to government insiders. Attempts by the FT to contact him have failed.
Mr Qubaisi comes from an influential family in the emirate said to be linked to the ruling al-Nahyan family by marriage. He emerged as one of Abu Dhabi's most active investors over the past decade, as the oil-rich emirate went on a corporate buying spree. He led Ipic's expansion from traditional conservative investments in foreign energy ventures into more exotic assets such as Virgin Galactic and Tesla Motors.
His other business interests included chairing Hakkasan Group, a leading nightclub and restaurant chain with branches in Las Vegas. He resigned from that post earlier this year.
Mr Qubaisi and Mr Husseiny have been under the spotlight since US authorities alleged last month that they conspired with some 1MDB officials to use a fake offshore company to siphon off part of the proceeds of a pair of 2012 bond issues by the Malaysian fund totalling about $3.5 billion.
The Ipic-guaranteed bonds were part of a growing relationship between Abu Dhabi and Malaysia, cemented in a March 2013 bilateral "strategic partnership" that led to another contentious $3 billion bond issue.
The 2012 and 2013 Ipic-guaranteed bond issues were arranged by Goldman Sachs, whose work on 1MDB is now being scrutinised by several US authorities. The bank has denied wrongdoing.
About $1.37 billion of the bond proceeds was transferred by 1MDB officials to a Swiss bank account belonging to a British Virgin Islands-registered business named Aabar Investments PJS Limited, US authorities have claimed.
The offshore shell company was allegedly named to give the impression that it was associated with Aabar Investments PJS, a subsidiary of Ipic based in Abu Dhabi. Mr Qubaisi and Mr Husseiny were allegedly directors of the BVI business. Ipic has since stated that it has no link to the offshore company,
Mr Qubaisi received almost $473 million of the diverted money into his accounts in 2012, the US court action claims. He allegedly used some of the funds to acquire US property worth about $100 million, including a New York penthouse.
Ipic is now battling 1MDB over a 2015 financing agreement under which the Abu Dhabi fund gave its Malaysian counterpart $1 billion in bailout loans in return for assets. Ipic announced in April that it was launching arbitration proceedings in London seeking $6.5 billion over an alleged default by 1MDB and the Malaysian finance ministry, which cosigned the deal. 1MDB has denied any wrongdoing.