Ryanair has been admitted to membership of the Nasdaq-100, joining just a handful of other non-US companies on the high-profile index.

The Nasdaq announced the annual membership changes after the close of US trading last night and the low-cost airline featured among the new companies admitted to the index.

It joins Sweden's Ericsson, Flextronics International of Singapore, Israel's Check Point Software Technologies and Teva Pharmaceutical Industries, an Israeli company that was added last month.

The move is expected to provide technical support for Ryanair's shares because about $30 billion is invested in funds tied to the index.

While it will primarily affect the company's Nasdaq-listed American Depositary Shares (ADSs), it could also have some knock-on impact on the ordinary shares listed in Dublin.

Analysts estimate that around 40 per cent of the stock is held in ADR form.

The news comes after a tough week for the airline following the announcement that the EU Commission had begun a formal investigation into whether concessions gained at its Belgian hub were illegal.

Although Ryanair dismissed the EU move, it has taken its toll on the share price which fell by 8 per cent over the course of the week.

The Nasdaq changes will come into effect from December 20th.

The overhaul is the first since Nasdaq announced new rules in October intended to change the index's membership more frequently and include more non-US companies.

The Nasdaq-100 is the basis for the most actively traded US equity issue.

About $30 billion is invested in funds tied to the index, most traded through an exchange-traded fund whose shares are known as the "Triple-Q" for its stock symbol, QQQ.

The Nasdaq has recently launched the EQQQ, a European version of the fund, which is registered in Ireland.

The fund, which will be marketed in Britain, Germany and Belgium as well as the Republic, was launched on December 2nd with Central Bank approval.