Luxembourg's district court in a statement said it had agreed to a request on Friday from Espirito Santo International (ESI) that it be placed under "controlled management".
Portugal has been thrown into turmoil since allegations emerged of accounting irregularities in ESI, owned by the high-profile Espirito Santo family, cast doubt on the strength of its economy.
Lisbon has admitted the crisis engulfing the giant Banco Espirito Santo group could affect Portugal's recovery after the country emerged from an international bailout in May.
President Anibal Cavaco Silva said the problems affecting the group "could have a certain affect on the real economy. . . and its creditors could be confronted with serious difficulties".
Portuguese authorities have also said they had opened several investigations into possible criminal offences related to BES and its entities.
BES' Swiss-based private banking arm Banque Privée Espirito Santo (BPES) and Compagnie Bancaire Helvétique (CBH) meanwhile said they had agreed to the sale of the former's client portfolio from Portugal, Spain and Latin America.
The two banks did not reveal details of the price tag or how many clients would come under CBH's wing.
BPES chief Jose Manuel Espirito Santo said the deal with CBH offered an "excellent solution" and that it was the best means to "defend the interests of our customers and staff".
Philippe Cordonier, head of CBH, said the deal marked a "significant step in the development of our bank" thanks to the expansion of its geographical reach.
CBH, a family-owned bank founded by financier Joseph Benhamou in 1991, is a relatively low-profile player in the Swiss private banking sector, which caters to ultra-wealthy clients from around the globe drawn by Switzerland's tradition of discretion.
Editor's note: this article was changed following a correction issued by AFP.