At a hearing in San Francisco federal court, US District Judge William Alsup said he was sceptical Waymo could ultimately prove that Uber's self-driving car programme used Waymo trade secrets. So far, Waymo had not uncovered convincing evidence that Uber copied its technology, he said.
"It is not the home run they were expecting to find," Alsup said.
However, Alsup said he would grant Waymo's request for more time to investigate documents and e-mails that Uber only recently disclosed. The trial had been scheduled to begin next week.
The case pits two companies battling to dominate the fast-growing field of self-driving cars.
Waymo claimed in a lawsuit earlier this year that former engineer Anthony Levandowski downloaded more than 14,000 confidential files before leaving to set up a self-driving truck company, which Uber acquired soon after.
Uber has denied using any of Waymo's trade secrets.
In court on Tuesday, Alsup said Waymo had solid evidence against Levandowski. However, Waymo decided to bring separate legal claims against Levandowski in private arbitration, and did not include him as a defendant in the lawsuit before Alsup.
Levandowski has asserted his constitutional rights against self-incrimination and refused to answer questions about the allegations.
"I think when Waymo got into this, they thought they would open (Uber's) files and find exact duplicates of Waymo," Alsup said.
"As it turns out, the product is dissimilar," he added.
Yet Alsup chided Uber lawyers for only recently disclosing to Waymo thousands of Levandowski emails, just before trial was set to begin.
"He's the most important witness in the case, and somehow his own files got overlooked?" Alsup said. "Very suspicious."
© Thomson Reuters 2017