Levandowski said he was not leaving Uber but would not participate in any of Uber's work on Lidar, according to an internal email to his employees first reported by Business Insider, which posted a copy of the email on its website. Uber confirmed the contents of the email to Reuters but declined to comment further.

Lidar is a technology critical to autonomous vehicles and at the heart of the lawsuit filed by Alphabet Inc's Waymo against Uber. Waymo is Levandowski's former employer.

According to the email, he will continue working on other parts of the self-driving car program such as software and operations.

Waymo in February sued Uber, alleging theft of its proprietary information on Lidar, which uses light pulses reflected off objects to gauge their position.

Waymo's lawsuit accuses Levandowski of stealing more than 14,000 confidential documents with information on Lidar designs before leaving the company to join Uber. Levandowski has not been named a defendant in the lawsuit.

Uber has denied the charges, and Levandowski in a recent deposition declined to answer most questions on the advice of his attorney.

The email did not give a reason for Levandowski stepping aside, but the decision came after a hearing in the case earlier this month in which U.S. District Judge William Alsup warned Uber that the evidence in the case could lead to an injunction barring Levandowski from working on Uber's self-driving car project.

Another hearing is scheduled for May 3 at which Waymo's request for an injunction on Uber's self-driving program is due to be considered.

Uber named Eric Meyhofer to replace Levandowski as head of its Advanced Technologies Group. Meyhofer, a roboticist, joined Uber in January 2015 from Carnegie Mellon University. He was part of a group of 40 faculty, researchers and technicians who Uber hired away from the school to help launch its self-driving program in Pittsburgh, Pennsylvania.

(Reporting by Heather Somerville and Dan Levine in San Francisco; Additional reporting by Gayathree Ganesan and Sangameswaran S in Bengaluru; Editing by Sai Sachin Ravikumar and Lisa Shumaker)

By Heather Somerville and Dan Levine