Qualcomm, the world's No. 1 mobile chipmaker, may face a European antitrust investigation in relation to a four-year-old complaint by a subsidiary of rival Nvidia Corp, three people familiar with the matter said on Tuesday.

An EU probe would come at an awkward time for Qualcomm, which is seeking to end an investigation by China's pricing regulator into monopoly practices.

British cellphone chipmaker Icera, acquired by Nvidia in 2011, took its grievances to the European Commission in June 2010, accusing Qualcomm of anti-competitive behaviour.

Details of the complaint were never made public. But another person familiar with the issue said Icera had accused Qualcomm of using patent-related incentives and exclusionary pricing of chipsets to discourage customers from doing business with Icera.

Until now, the issue appeared to have faded from the Commission's agenda.

But regulators decided to fast-track the case after Europe's second-highest court in June upheld a record 1.1 billion euro EU fine against U.S. chipmaker Intel for abuse of its dominant market position, according to one of the sources.

It is not unusual for the EU competition authority to take several years to build a case before opening an investigation.

"The Commission may open a case after the summer," said the source, who declined to be named because of the sensitivity of the matter.

The Commission's spokesman for competition policy, Antoine Colombani, declined to comment, as did Qualcomm. Companies can be fined as much as 10 percent of their global revenues for breaching EU antitrust rules.

In 2010, the EU competition authority scrapped a four-year probe into Qualcomm after Swedish mobile telecom gear maker Ericsson and U.S. rival Texas Instruments withdrew their objections against the company.

(Reporting by Foo Yun Chee; editing by Tom Pfeiffer)