SAN FRANCISCO – Attorneys from Morrison & Foerster may have to take the stand in the fast-approaching trade secrets trial between Google Inc.’s driverless car unit Waymo and Uber to explain why the law firm remained silent about possessing an ex-Waymo engineer’s documents.

U.S. District Judge William Alsup of the Northern District of California on Wednesday sharply rebuked Uber Technologies Inc.’s lawyers at MoFo for not informing him earlier it had the documents in its possession. The files are potentially key to Waymo’s allegations that Uber is ripping off its driverless car technology.